视频进化

Video Evolution

正如多年来这种媒介的用途发生了变化一样，它的物理性质也发生了变化。视频信号最初是模拟信号，后来发展成为具有不同类型数字格式的数字信号。电视刚问世时，照相机和电视机需要很大的空间来容纳模拟世界的原始电子管技术。在当今的数字社会中，随着质量的不断提高，相机尺寸和媒体文件不断变小。

Just as the use of this medium has changed over the years, so has its physical nature evolved. The video signal started as analog and has developed into digital with different types of digital formats. When television was first created, cameras and television sets required a great deal of room to house the original tube technology of the analog world. In today’s digital society, camera size and media files continue to get smaller as the quality continues to improve.

例如，当本书首次出版时，高清正成为首选格式。现在业界正在制作超高清 (4K) 节目，其分辨率是高清的两倍多。这种分辨率和易用性的扩展导致许多制作人为他们的项目选择数字途径而不是胶片拍摄。

For example, when this book was first published, High Definition was becoming the format of choice. Now the industry is creating programming in Ultra High Definition (4K), which has over twice the resolution of High Definition. This expansion in resolution and ease of use has caused many producers to choose the digital route over shooting on film for their projects.

尽管设备发生了变化，但视频信号产生过程中的一些过程仍然保持不变。这使得视频从模拟到数字的发展不仅对研究很有趣，而且有助于提供当前数字视频世界运行所依赖的知识基础。当今的许多数字技术之所以如此，是因为它是从模拟技术发展而来的。

Although the equipment has changed, some of the processes involved in the origination of the video signal have remained the same. This makes the progression of video from analog to digital not only interesting to study, but helpful in providing a foundation of knowledge upon which the current digital video world operates. So much of today’s digital technology is the way it is because it evolved from analog.

模拟和数字

Analog and Digital

让我们考虑一下模拟和数字领域。来自物理世界的所有信息都是模拟的。漂浮的云、海浪和军乐队的声音都存在于构成人类体验的频率范围内。这个频谱可以被任何数量的数码相机捕获，并且 录音设备，然后转换为任意数量的数字文件类型，这些文件类型由代表图像或声音的数字数据或零和一组成。

Let’s consider the analog and digital realms. All information from the physical world is analog. A cloud floating by, an ocean wave, and the sounds of a marching band all exist within a spectrum of frequencies that comprise human experience. This spectrum of frequencies can be captured by any number of digital cameras and recording equipment and then translated to any number of digital file types made up of digital data, or zeros and ones, representing the image or sound.

图 1.1 从模拟到数字再到模拟

Figure 1.1 From Analog to Digital to Analog

然而，人类不会处理数字数据的零和一。最终，这些数据必须被转换回模拟形式，这样我们人类才能看到和听到它。即使使用数字家庭接收器和其他观看或收听设备，数字信号的 0 和 1 最终也必须以模拟形式再现，以便人类通过视觉和听觉体验它（图 1.1 ）。

Human beings, however, do not process the zeros and ones of digital data. Eventually that data must be converted back to an analog form so we humans can see and hear it. Even with a digital home receiver and other viewing or listening devices, the zeros and ones of a digital signal must eventually be reproduced as analog for humans to experience it with their sight and sound senses (Figure 1.1).

信号再现

Signal Reproduction

在电视的早期，视频是基于机械概念在录像机上以模拟信号的形式录制和再现的。录像机沿着导轨移动录像带，并通过记录或播放信号的磁头。由于录像带在机械系统中移动，信息只能按照创建时的顺序进行记录或复制。这使得录像带的后期制作，或内容拍摄后的编辑和操作成为一个线性过程，无法即时访问。

In the early days of television, video was recorded and reproduced as an analog signal on a videotape machine, which was based on mechanical concepts. The videotape machine moved the videotape along guides and through magnetic heads that recorded or played back the signal. As a result of the videotape moving through a mechanical system, the information could only be recorded or reproduced in the order in which it was created. This made post production of videotape, or the editing and manipulating of content after it was shot, a linear process with no instant access.

图 1.2 模拟录像带录制与数字视频制作

Figure 1.2 Analog Videotape Recording vs Digital Video Production

随着数字技术的出现，信号再现的主要系统变成了固态电子设备，包括计算机、服务器和数字卡。这种变化创造了一个基于计算机文件的系统，而不是模拟时代基于磁带的机械系统。基于文件的系统允许随机或非线性地访问信息，而无需考虑信息的生成顺序或信息在存储介质中的位置（图 1.2 ）。

With the advent of digital, the primary system for signal reproduction has become solid-state electronics, incorporating computers, servers and digital cards. This change has created a computer file-based system, rather than the taped-based mechanical system of the analog era. File-based systems allow random, or nonlinear, access to information without respect to the order in which it was produced or its placement within the storage medium (Figure 1.2).

虽然大多数有线电视公司、广播电台、互联网公司以及制作或后期制作设施使用基于数字文件的系统来创建、编辑和传输视频信号，但一些设施仍然使用旧的录像机来包含遗留（模拟）内容。

While most cable companies, broadcast stations, Internet companies, and production or post production facilities create, edit and transmit video signals using a digital file-based system, some facilities still have older videotape machines for inclusion of legacy (analog) content.

关于本书

About This Book

为了创建视频过程的完整图景并回答“视频是如何工作的？”这个问题，本书首先研究了模拟视频信号。数字视频技术是模拟系统的直接演变。在进入讨论之前，了解模拟系统可为您打下坚实的基础数字化，以及视频在数字分发新时代的运作方式。

To create a complete picture of the video process—and answer the question “How does video work?”—this book begins by examining the analog video signal. Digital video technology is a direct evolution from the analog system. Having the knowledge of the analog system provides a firm foundation before moving into a discussion of digital, and how video works today in the new age of digital distribution.

虽然本书旨在涵盖在专业环境中创建、存储和传输视频信号的过程，但相同的信息和概念适用于任何视频工具，包括消费设备。

While this book is designed to cover the process of creating a video signal, storing it, and transmitting it in a professional environment, the same information and concepts apply to any video tool, including consumer equipment.

套筒相机

Tube Cameras

虽然电子管拾取器已被数字技术取代，但电子管使用的扫描图像的过程对当前系统有影响。

While the tube pickup has been replaced with digital technologies, the process of scanning the image that the tube used has implications for current systems.

在视频管相机中，镜头将图像聚焦在相机内部拾取管的表面上。拾取管的表面称为目标（图 2.1）。目标是感光的，就像 片子。当光线照射到目标的表面时，它会根据照射到其表面的光量按比例导电。如果目标的脸上没有光，目标就会抵抗电流。

In a video tube camera, the lens focuses the image on the face of a pickup tube inside the camera. The face of the pickup tube is known as the target (Figure 2.1). The target is light-sensitive, like a piece of film. When light shines on the face of the target, it conducts electricity in proportion to the amount of light that is striking its surface. Without light on the face of the target, the target resists the flow of electricity.

图 2.1 (A)相机聚焦图像和(B)套筒相机目标区域

Figure 2.1 (A) Camera Focusing on Image and (B) Tube Camera Target Area

电子流，称为束，来自管的后端，并在拾取管内部的目标表面上来回扫描。生成的电流是否允许从目标传递到相机输出端，具体取决于目标表面的电阻大小。

A stream of electrons, called the beam, comes from the back end of the tube and scans back and forth across the face of the target on the inside of the pickup tube. The electrical current generated is either allowed to pass from the target to the camera output or not, depending on the amount of resistance at the face of the target.

阻力的大小取决于照射在目标上的光量。从目标流出的电信号实际上是来自相机所瞄准场景的光的电子再现。

The amount of resistance varies depending on how much light is shining on the target. The electrical signal that flows from the target is, in effect, the electronic re-creation of the light coming from the scene at which the camera is aimed.

扫描图像

Scanning the Image

当相机看到一个物体时，它就会开始扫描图像。电子束在靶的内表面来回扫过。在电子束撞击目标表面的地方，它照亮了与电子束大小相同的区域（图 2.2）。产生的电信号是变化电压的连续流动，代表击中目标的光。如果没有关于扫描点位置的信息，接收器就无法知道图片的开始和结束位置。在后面的章节中，我们将看到这是如何实现的。

When a camera sees an object, it begins scanning the image. The beam of electrons sweeps back and forth across the inside face of the target. Where the electron beam strikes the face of the target, it illuminates an area the same size as the electron beam (Figure 2.2). The resulting electrical signal is a continuous flow of varying voltages representing the light that struck the target. Without some information about where the scanning dot was positioned there would be no way for the receiver to know where to start and end the picture. In a later chapter we will see how that is accomplished.

图 2.2 扫描和复制图像

Figure 2.2 Scanning and Reproducing an Image

图 2.3 放大图片元素

Figure 2.3 Magnified Picture Elements

在美国使用的电视系统中，电子束在每个电视帧中会在目标上来回扫描 525 次。因此，电视信号中的每一帧都由 525 条扫描线组成。相机的尺寸或摄像管或监视器的尺寸都无关紧要。从帧顶部到帧底部扫描的总行数始终为 525。

In the television system that was used in the United States, the electron beam would scan back and forth across the target 525 times in each television frame. Thus each frame in the television signal was composed of 525 scan lines. It did not matter what size the camera was or what size the pickup tube or monitor was. The total number of lines scanned from the top of the frame to the bottom of the frame would always be 525.

在摄像机中创建的图像现在已经变成了不同电压的电子信号。作为一种电子信号，电视图像可以通过电缆传输、记录，甚至通过空气传输。

The image created in the video camera had now been turned into an electronic signal of varying voltages. As an electronic signal, the television image can be carried by cables, recorded, or even transmitted through the air.

显示图像

Displaying the Image

相机产生的变化电压可以转换回光。这种电能为电视接收器或监视器中的电子枪提供动力。那支枪将电子流发送到接收器中显像管的表面。视频信号中不断变化的电压导致接收管内表面上的化学磷光体在直接方向上发出强烈的光与电压量成正比。因此，逐行重新创建源自管式相机的图像。动作和细节都被再现。

The varying voltages generated by the camera could be converted back into light. This electrical energy powered an electron gun in the television receiver or monitor. That gun sent a stream of electrons to the face of the picture tube in the receiver. Changing voltages in the video signal caused chemical phosphors on the inside face of the receiver tube to glow with intensity in direct proportion to the amount of voltage. The image that originated in the tube camera is thus recreated, line by line. Motion and detail were all reproduced.

相机芯片

Camera Chips

多年来，驱动管式照相机所需的摄像管和扫描轭已经被淘汰，取而代之的是光敏芯片（图 2.4）。芯片摄像头拾音器常用的技术有两种，CCD和CMOS。CCD 是一种电荷耦合器件。CMOS 是互补金属-氧化物-半导体的简称。这项技术最初出现在静态相机中，现在在摄像机中也很常见。

Over the years, the pickup tubes and the scanning yokes needed to drive the tube cameras have been eliminated and replaced by light-sensitive chips (Figure 2.4). There are two technologies commonly used for chip camera pickups, CCD and CMOS. CCD is a charge-coupled device. CMOS is short for complementary metal – oxide–semiconductor. First found in still cameras, this technology is now also common in video cameras as well.

图 2.4 CCD 相机对焦图像

Figure 2.4 CCD Camera Focused on Image

CCD 是一种芯片，包含一个区域或站点，上面覆盖着数百万个微型电容器或电容器（用于存储电能的设备）。图像传感器芯片上有数百万个单独的站点。芯片通常根据“百万像素”的数量或它包含的数百万像素来评定。该芯片源自为 EPROM（可擦除可编程只读存储器）芯片开发的技术。它们用于可能发生更新或更改的计算机软件。当信息被烧录到 EPROM，它的意思是半永久性的。只有在高强度紫外线下才能擦除。

A CCD is a chip that contains an area, or site, covered with millions of tiny capacitors or condensers (devices for storing electrical energy). There are millions of individual sites on image sensor chips. Often a chip is rated by the number of “megapixels” or millions of pixels it contains. This chip came out of the technology that was developed for EPROM (Erasable Programmable Read-Only Memory) chips. They are used for computer software where updates or changes can occur. When the information is burned onto an EPROM, it is meant to be semi-permanent. It is erasable only under high-intensity ultraviolet light.

在 CCD 相机中，转换为电能的光信息存储在芯片上的位置上。然而，与 EPROM 不同的是，它很容易移除或更改。这些地点是微型电容器，可以容纳电荷，并通过绝缘材料彼此隔开。这可以防止电荷泄漏。该芯片非常高效，可以长时间保存信息。当这些位置完成曝光后，它们收集的电荷将移动到相邻的保持单元，准备传递到芯片外处理。

In a CCD camera, the light information that is converted to electrical energy is deposited on sites on the chip. Unlike an EPROM, however, it is easily removed or changed. The sites are tiny condensers that hold an electrical charge and are separated from each other by insulating material. This prevents the charge from leaking off. The chip is very efficient and can hold the information for extended periods of time. When the sites are done being exposed, the charges they collected are moved to adjacent holding cells ready to be passed onto off-chip processing.

CMOS 芯片类似于 CCD，但具有直接内置于图像捕获芯片中的放大和扫描电路。结合一些电路可以生产更便宜的相机。然而，当他们在拍摄图像时传输图像，可能会出现称为“滚动快门”的伪影。为此，高端相机仍然使用帧传输CCD芯片。

CMOS chips are similar to CCDs but have amplification and scanning circuits built directly into the image capture chip. Combining some of the circuits makes it possible to produce less expensive cameras. However, as they transfer the image as it is being photographed, an artifact known as “rolling shutter” may occur. For this reason, high-end cameras still use frame transfer CCD chips.

芯片相机的类型

Types of Chip Cameras

芯片相机有多种形式，从手机中的微型相机到电影和电视制作中最大的摄影棚相机。在芯片相机内部，通过镜头的光线聚焦在芯片上。对于使用多个芯片的相机，进入相机的光会通过分束器，然后聚焦到芯片上，而不是通过一个或多个拾取管。分束器是一种光学设备，它吸收通过透镜进入的光并将其分开或分开。它引导光线通过过滤器，过滤掉每个芯片的一种颜色以外的所有颜色。一个芯片只能看到红光，一个只能看到蓝光，一个只能看到 绿色的。这些滤光片被称为二向色滤光片，因为它们会滤除三种颜色中的两种。这些芯片是光敏集成电路（图 2.5）。

Chip cameras can be found in many forms, from the tiny camera in phones to the largest studio cameras in film and television production. Inside the chip camera, light coming through the lens is focused on a chip. In the case of cameras that use multiple chips, light entering the camera goes through a beam splitter and is then focused onto the chips, rather than passing through a pickup tube or tubes. A beam splitter is an optical device that takes the light coming in through the lens and divides or splits it. It directs the light through filters that filter out all but one color for each of the chips. One chip sees only red light, one only blue, and one only green. The filters are called dichroic because they filter out two of the three colors. These chips are photosensitive, integrated circuits (Figure 2.5).

图 2.5 三片式 CCD

Figure 2.5 Three-Chip CCD

当光线照射到芯片上时，它会根据照射到芯片上的光量按比例为芯片位置充电。换句话说，聚焦在芯片上的图像被光敏表面捕获为电荷。然后从芯片上读取该电荷。这些芯片背后的技术使它们能够在不超载的情况下发射强光。但是，如果光线足够亮，电荷可能会从一个位置溢出到另一个位置。这会导致图像中对象的边缘模糊或滞后。

When light strikes the chip, it charges the chip’s sites with electrical energy in proportion to the amount of light that strikes the chip. In other words, the image that is focused on the chip is captured by the photosensitive surface as an electrical charge. This electrical charge is then read off the chip. The technology behind these chips allows them to shoot bright light without overloading. However, if the light is bright enough, the charge can spill over from one site to the next. This can cause the edges of an object within an image to smear or lag.

为防止这种情况，在芯片表面放置光栅或黑屏，以便在感光点之间存在绝缘材料和吸光材料。为了捕获存储在芯片上的信息，芯片被从一个位置扫描到另一个位置，并在发生这种情况时释放能量。根据电能的多少，在扫描每个站点时分配一个数值展示。这是数字化过程的一部分，因为数值被转换为计算机数据以供存储和传输。

To prevent this, an optical grid or black screen is laid over the face of the chip so that between the light-sensitive sites there is both insulation and light-absorbing material. To capture the information stored on the chip, the chip is scanned from site to site, and the energy is discharged as this happens. A numerical value is assigned as each site is scanned, according to the amount of electrical energy present. This is part of the digitizing process, as the numerical value is converted to computer data for storage and transmission.

许多相机采用单芯片设计。单芯片相机在每个照片点上都有滤镜，只让一种颜色通过；红色、蓝色或绿色。最常见的方法是使用一种称为拜耳滤镜的格式，它是一种图案中的颜色排列，其绿色像素数量是红色或蓝色像素的两倍。这说明了人类视觉，它对色谱的绿色区域更敏感。在单芯片相机中，不需要三个芯片和一个分束器。

Many cameras use a single-chip design. The single-chip camera has filters over each photo site that pass only one color; red, blue or green. The most common method for this uses a format called the Bayer filter, which is an arrangement of the colors in a pattern that features twice as many green pixels as red or blue. This accounts for human vision, which is more sensitive to the green region of the color spectrum. In a single-chip camera, there is no need for three chips and a beam splitter.

通常，相机中芯片的尺寸越大，图像质量越好。例如，具有 ⅔ 英寸芯片的相机将比具有 ½ 英寸芯片的相机捕捉到质量更好的图像。

Typically, the larger the size of the chip in the camera, the better the image quality. For example, a camera with a ⅔ inch chip will capture a better quality image than a camera with a ½ inch chip.

视频线

Video Lines

在管式照相机中，电子束将光图像转换为电子信号。然后，CRT 视频接收器或监视器中的电子束会导致称为磷光体的化学物质发光，从而将电信号转换回光信号。

In a tube camera, the electron beam transforms a light image into an electronic signal. Then, an electron beam within a CRT video receiver or monitor causes chemicals called phosphors to glow so they transform the electrical signal back into light.

当电视系统最初构想于 1930 年代后期时，此过程的规范已由国家电视系统委员会 (NTSC) 标准化。NTSC 标准用于北美以及亚洲和拉丁美洲的部分地区。作为其他国家开发了自己的电视系统，创建了其他视频标准。东欧和西欧使用一种称为 PAL（Phase Alternate Line）的系统。法国和前苏联国家使用称为 SECAM（Séquential Color Avec Mémoire，或带记忆的顺序颜色）的系统。大多数发达国家已转而使用数字标准传输电视，从而使这些模拟格式过时。然而，世界上仍有一些地方仍然存在模拟广播。

The specifications for this process were standardized by the National Television System Committee, or NTSC, when the television system was originally conceived in the late 1930s. The NTSC standard was used in North America and parts of Asia and Latin America. As other countries developed their own television systems, other video standards were created. Eastern and Western Europe used a system called PAL (Phase Alternate Line). France and the countries of the former Soviet Union used a system known as SECAM (Séquential Colour Avec Mémoire, or Sequential Color with Memory). Most developed countries have switched to transmission of television using digital standards, making these analog formats obsolete. However, there are still places in the world where analog broadcasts remain.

对于每个 NTSC 视频帧，电子束总共扫描了 525 行。每秒扫描 30 帧，这意味着每秒扫描总共 15,750 行（黑白视频）（30 帧 x 每帧 525 行）。这个速率被称为线路频率。每秒扫描 15,750 行的速度如此之快，以至于人眼根本不会注意到行进的光束。随着电子束扫描每帧 525 行，视频图像不断刷新。一旦一帧完全显示，扫描就开始下一帧，因此整个过程对观众来说是无缝的。

For each NTSC video frame, the electron beam scanned a total of 525 lines. There were 30 frames scanned each second, which means that a total of 15,750 lines (black and white video) were scanned each second (30 frames x 525 lines per frame). This rate was called the line frequency. Scanning 15,750 lines per second is so fast that the eye never notices the traveling beam. The video image is constantly refreshed as the electron beam scans the 525 lines in each frame. As soon as one frame is completely displayed, scanning begins on the next frame, so the whole process appears seamless to the viewer.

NTSC 行频和帧速率随着颜色的添加而改变。PAL 和 SECAM 都以每秒 25 帧的速度每帧使用 625 行。这两个系统是在引入彩色电视之后开发的，因此不需要任何额外的更改。存在试图结合所有这些标准的最佳元素的变体和组合。

The NTSC line frequency and frame rate changed with the addition of color. Both PAL and SECAM used 625 lines per frame at 25 frames per second. These two systems were developed after the introduction of color television and consequently did not require any additional changes. There are variations and combinations that attempt to combine the best elements of all of these standards.

冲裁

Blanking

扫描显像管的电子束就像一台旧打字机。它只在一个方向上起作用。当它到达一行视频的末尾时，它必须折回或返回到屏幕的另一边以开始下一行。同样，当它到达图像底部时，它必须回溯或回到图像顶部以开始扫描下一帧（图 3.1）。

An electron beam scanning a picture tube is like an old typewriter. It works in only one direction. When it reaches the end of a line of video, it must retrace or go back to the other side of the screen to start the next line. Likewise, when it reaches the bottom of the image, it must retrace or go back to the top of the image to begin scanning the next frame (Figure 3.1).

电子束回溯以开始扫描或追踪下一行的时间段是称为水平消隐的较大时间间隔的一部分。电子枪回溯到图像顶部开始扫描另一帧的时间称为垂直消隐。在水平或垂直消隐期间，电子束被消隐或关闭，以免引起任何电压流动。这样回溯是不可见的。

The period of time during which the electron beam retraces to begin scanning or tracing the next line is part of a larger time interval called horizontal blanking. The period of time that the electron gun is retracing to the top of the image to begin scanning another frame is called vertical blanking. During horizontal or vertical blanking, the beam of electrons is blanked out or turned off, so as not to cause any voltage to flow. This way the retrace is not visible.

图 3.1 扫描回溯

Figure 3.1 Scanning and Retracing

图 3.2 视频帧

Figure 3.2 Video Frame

水平消隐间隔是连续行之间的间隔。垂直消隐间隔是连续帧之间的间隔。由于视频图像与其他图像相结合，使用视频编辑系统或视频切换器等设备，从源到源的变化发生在绘制完整图像后的垂直消隐间隔期间。这可以比作在胶片画幅的画框线上拼接。

The horizontal blanking interval is the separation between consecutive lines. The vertical blanking interval is the separation between consecutive frames. As the video image is integrated with other images, using equipment such as video editing systems or video switchers, the change from source to source occurs during the vertical blanking interval after a complete image has been drawn. This can be compared to splicing on the frame line of a film frame.

水平消隐实际上发生在每行视频信息开始之前的稍前。垂直消隐发生在每一帧之后。视频画面本身被称为活动视频（图 3.2）。在 NTSC 系统中，活动视频使用一帧中包含的 525 行中的 480 行。PAL 和 SECAM 使用 625 条总线路中的 580 条有效线路。消隐用作活动视频周围的图片框。它是电视信号的必要组成部分，即使电子束被关闭。

Horizontal blanking actually occurs slightly before the beginning of each line of video information. Vertical blanking occurs after each frame. The video picture itself is referred to as active video (Figure 3.2). In the NTSC system, active video uses 480 out of the 525 lines contained in one frame. PAL and SECAM use 580 active lines out of the 625 total lines. Blanking functions as the picture frame around the active video. It is a necessary component of the TV signal, even though the electron beam is shut off.

视觉暂留

Persistence of Vision

电影以每秒 24 帧的速度拍摄。但是，如果以该速率投影，运动图像的闪烁质量将是显。闪烁是让我们首先感知电影中运动的现象的结果。这种现象称为视觉暂留。

Film is shot at 24 frames per second. However, if it were projected at that rate, a flickering quality to the moving image would be noticeable. The flickering is a result of the phenomenon that lets us perceive motion in a movie in the first place. That phenomenon is called persistence of vision.

图 3.3 西洋镜

Figure 3.3 Zoetrope

视觉暂留是指视网膜，即人眼的感光部分，将暴露在其面前的图像保留一定时间。当眼睛等待接收下一张图像时，该图像会逐渐消失。保留的阈值是 1/30 到 //32 秒。如果图像在视网膜上的变化速度比这慢，眼睛就会看到光，然后是黑暗。如果图像以更快的速度变化，眼睛会将图像视为连续运动而不是单个图像。这个概念是 19 世纪开发的一种称为 Zoetrope 的设备的基础（图 3.3）。经过 通过纺车上的一个小缝隙观看一系列静止图像，图像中的人物似乎在移动。

Persistence of vision means that the retina, the light-sensitive portion of the human eye, retains the image exposed to it for a certain period of time. This image then fades as the eye waits to receive the next image. The threshold of retention is 1/30 to //32 of a second. If the images change on the retina at a rate slower than that, the eye sees the light and then the dark that follows. If the images change at a faster rate, the eye sees the images as continuous motion and not as individual images. This concept was the basis of a device developed in the 19th century called the Zoetrope (Figure 3.3). By viewing a series of still images through a small slit in a spinning wheel, the characters in the images appeared to move.

在电影中，通过简单地将每一帧放映两次来利用这个概念。电影放映机闸门里的画面被按住，快门开了两次。然后胶片移动到下一帧，快门再次显示图像两次。这样，当投影仪以每秒 24 帧的速度运行时，每秒显示 48 帧，并且眼睛感知平滑、连续的运动。

In film, this concept is exploited by simply showing each frame twice. The picture in the gate of the film projector is held, and the shutter opens twice. Then the film moves to the next frame and the shutter again reveals the picture twice. In this way, 48 frames per second are shown while the projector runs at 24 frames per second, and the eye perceives smooth, continuous motion.

领域

Fields

每秒 30 帧的视频帧速率可能会使不断变化的帧的闪烁变得明显。因此，需要提高帧速率。最简单的方法是将帧速率加倍至每秒 60 帧。这在电子管电子学的早期是一项技术挑战。当时的工程师通过将他们能够捕获的 30 帧分解为 60 个称为场的半帧来解决这个问题，每个场包含帧的交替扫描线。

The 30-frames-per-second frame rate of video could potentially allow the flicker of the changing frames to be noticeable. Therefore, the frame rate needed to be increased. The simplest way to do this would be to double the frame rate to 60 frames per second. This was a technological challenge in the early days of tube electronics. The engineers of the time solved the problem by breaking the 30 frames they were able to capture into 60 half frames called fields, each field containing alternating scan lines of the frame.

摄像头处理电路每隔一行读取视频帧。由于有 525 行构成一个完整的帧，即 1/30 秒，每隔一行扫描一次会产生每场扫描 262½ 行，即 1/60 秒（图 3.4 ）。两场 262½ 行的每场组合起来构成 525 行，或一个完整的帧（图 3.5）。PAL 和 SECAM 中的过程相同，考虑到它们的线路和帧速率。

The pickup camera processing circuits read out every other line of the video frame. Since there are 525 lines that make up a complete frame, or 1/30 of a second, scanning every other line yields 262½ lines scanned per field, or 1/60 of a second (Figure 3.4). Two fields of 262½ lines each combine to make 525 lines, or one complete frame (Figure 3.5). The process was the same in PAL and SECAM, taking into consideration their line and frame rates.

隔行扫描

Interlace Scanning

这种逐场扫描的过程称为隔行扫描，因为每个场中的行与交替行交错

The process of this field-by-field scanning is known as interlace scanning because the lines in each field interlace with the alternate

图 3.4 隔行扫描

Figure 3.4 Interlace Scanning

图 3.5 交错帧

Figure 3.5 Interlaced Frame

其他字段的行。每个帧有两个字段。因为图像以 1/60 秒的速度出现，所以眼睛看不到两个场之间的间隔。因此，眼睛感知连续运动。

lines of the other field. There are two fields for each frame. Because the images are appearing at the rate of 1/60 of a second, the eye does not see the interval between the two fields. Therefore, the eye perceives continuous motion.

这种针对 80 年前问题的巧妙解决方案现在对当今的内容创作者提出了挑战。虽然一些广播标准仍然指定隔行扫描，但许多图像显示设备不再需要交替行。这些格式被称为“逐行”，因为每一行都被扫描，一条接一条，没有隔行扫描。当隔行扫描的材料呈现在逐行显示器上时，它可能会导致一种称为梳理的分散注意力的伪像。这会留下从快速运动区域延伸的细线，类似于梳齿（图 3.6）。

This ingenious solution to a problem from 80 years ago now presents a challenge to today’s content creators. While some broadcast standards still specify interlaced scanning, many image display devices no longer require alternating lines. These formats are called “progressive” as each line is scanned, one after the other, without interlacing. When interlaced material is presented on progressive displays, it can lead to a distracting artifact called combing. This leaves fine lines extending from areas of fast motion similar to the teeth of a comb (Figure 3.6).

当前的数字系统以多种不同的帧速率进行扫描，具体取决于世界标准和图像内容，这将在第 12 章中讨论。在美国，一些广播公司使用基于 60 Hz 功率标准的大约每秒 30 帧的帧速率。其他国家可能使用 60 赫兹或 50 赫兹的电力， 欧洲标准。那些使用 50Hz 电源的通常每秒播放 25 帧。许多戏剧作品使用每秒 24 帧来匹配电影帧速率标准的外观。体育制作促使一些网络使用每秒 60 帧的速度在快速移动的材料上进行更清晰的运动。

Current digital systems scan at a number of different frame rates, depending on world standards and image content, which is discussed in Chapter 12. In the U.S., some broadcasters use frame rates at about 30 frames per second, based on the 60 Hz power standard. Other countries might use 60 Hz or 50 Hz electricity, the European standard. Those that use 50Hz power often broadcast 25 frames per second. Many dramatic productions use 24 frames per second to match the look of the film frame rate standard. Sports production drives some networks to use 60 frames per second for sharper motion on fast moving material.

图 3.6 梳理伪影

Figure 3.6 Combing Artifact

同步信号

Synchronizing Signals

当视频从源移动到监视器时，它是一系列电脉冲。无论是模拟还是数字，通过电线、光纤还是通过空气，构成图像的脉冲一个接一个地跟随。如果您可以冻结时间，然后查看信号路径上的各个点，则可以测量各个电压或找到构成像素的位。那么传输介质是单一维度的。它只有长度，没有深度或宽度。

As video moves from source to monitor, it is a series of electrical impulses. Whether analog or digital, by wire, fiber optic or through the air, the pulses that make up the picture follow each other one after the other. If you could freeze time then look at individual points along the signal path, you could measure individual voltages or find the bits to make pixels. The transmission medium then is a single dimension. It has only length, but not depth or width.

另一方面，单帧视频既有宽度又有高度。您可以在屏幕左侧和右侧之间的某个点从信号路径中找到特定像素。它也是距顶部和底部的可测量距离。所以一个框架是一个二维的图像。电影是由一个接一个显示的二维帧组成的。您可以将其视为三维。

On the other hand, a single frame of video has both width and height. You can find a specific pixel from the signal path at some point between the left and right of the screen. It also is a measurable distance from the top and bottom. So a frame is a two-dimensional image. Motion pictures are made of the two-dimensional frames being shown one after the other. You can think of this as a third dimension.

同步信号提供驱动扫描的信息，将三维图像变为串行形式以供传输和存储。然后可以使用相同的信号重建图片以便查看。

Synchronizing signals provide the information to drive the scanning that changes the three dimensional images to a serial form for transmission and storage. The same signals can then be used to rebuild the pictures so they can be viewed.

当在同一系统中使用多个来源时，例如电视演播室中的摄像机，每个来源都必须在同一时刻开始扫描。虽然大部分视频处理已过渡到数字信号，但模拟同步仍普遍用于整个演播室和远程制作。尽管数字设备以不同的方式处理同步，但仍使用下面描述的相同同步信号来协调该过程。

When multiple sources are used in the same system, like the cameras in a TV studio, each must start their scan at the same exact moment. While most of video process has transitioned to digital signals, analog sync is still commonly used throughout studio and remote production. Although digital devices process sync in a different manner, the same sync signals described below are still used to co-ordinate the process.

同步发电机

Synchronizing Generators

同步发生器，或称同步发生器，是模拟视频系统的核心。同步发生器产生许多不同的脉冲来驱动早期模拟设备的扫描。随着电子设备从电子管过渡到固态，许多照相机、录像机和处理设备开始采用自己的同步发生器电路。主屋同步发生器还向具有自己的同步发生器的设备提供信号。从属于该主信号的设备被认为是同步锁定的。

A synchronizing generator, or sync generator as it is called, was the heart of the analog video system. Sync generators created a number of different pulses for driving the scanning of early analog equipment. As electronics transitioned from tubes to solid state, many cameras, recorders and processing devices began to incorporate their own sync generator circuits. The master house sync generator also provides a signal to devices that have their own sync generators. Devices that slave to that master signal are considered to be genlocked.

同步发生器的核心是一个振荡器，它发出一个称为颜色副载波的信号，它是承载信号颜色信息部分的参考信号（本章稍后将更详细地讨论）。彩色副载波的频率 是每秒 3,579,545 个周期，四舍五入，通常简称为 3.58。从这个基本信号开始，同步发生器通过电子乘法和除法过程输出其他频率，以产生驱动视频设备所需的其他脉冲。这些脉冲包括水平和垂直同步脉冲、水平和垂直驱动脉冲、水平和垂直消隐脉冲以及均衡脉冲（图 4.1）。

The heart of the sync generator is an oscillator that put out a signal called the color subcarrier, which is the reference signal that carries the color information portion of the signal (discussed in more detail later in this chapter). The frequency of the color subcarrier is 3,579,545 cycles per second, rounded off and more commonly referred to as simply 3.58. Starting with this basic signal, the sync generator, through a process of electronic multiplication and division, outputs other frequencies in order to create the other pulses that are necessary for driving video equipment. These pulses included horizontal and vertical synchronizing pulses, horizontal and vertical drive pulses, horizontal and vertical blanking pulses, and equalizing pulses (Figure 4.1).

图 4.1 同步发生器

Figure 4.1 Sync Generator

这些脉冲通常组合在一起，因此一个信号将包含多个同步分量。组合信号称为复合信号。复合消隐和复合视频等术语指的是此类信号。

These pulses are often combined so that one signal will contain multiple synchronizing components. Combination signals are referred to as composite signals. Terms such as composite blanking and composite video refer to such signals.

同步脉冲

Synchronizing Pulses

对于较旧的模拟系统，同步发生器会同时输出水平和垂直同步脉冲。这些同步脉冲确保系统内的所有设备都及时或同步。水平和垂直同步脉冲是复合信号的一部分，因此它们可以很容易地馈送到任何需要同步参考信号的设备。

For older analog systems, the sync generator put out both horizontal and vertical synchronizing pulses. These synchronizing pulses ensured that all of the equipment within the system was in time or synchronized. Horizontal and vertical synchronizing pulses are part of the composite signal, so they can be easily fed to any piece of equipment that requires a sync reference signal.

水平同步脉冲出现在每行模拟视频的开头。他们确保监视器和接收器与摄像机正在创建的信息逐行同步。在垂直间隔期间出现垂直同步脉冲。这些脉冲确保回扫正确进行，因此枪处于正确的位置以绘制下一个场的开始。

Horizontal synchronizing pulses appeared at the beginning of each line of analog video. They assured that monitors and receivers were in synchronization on a line-by-line basis with the information that the camera was creating. Vertical synchronizing pulses appeared during the vertical interval. These pulses assured that the retrace was taking place properly, so that the gun was in its proper position for painting the beginning of the next field.

复合同步信号确保每台设备都在系统内逐行、逐场运行。如果设备不同步，图像之间的切换会导致监视器中的图像失去稳定性。例如，溶解和特殊效果可以改变颜色或移动位置。字符生成器或计算机生成的图像可能会出现在图像中与其最初放置的位置不同的位置。

The composite sync signal ensures that each piece of equipment is operating within the system on a line-by-line, field-by-field basis. If equipment is not synchronized, switching between images can cause the image in the monitor to lose stability. For example, dissolves and special effects can change color or shift position. Character generators or computer-generated images might appear in a different position in the image from where they were originally placed.

彩色副载波

Color Subcarrier

如上所述，随着彩色电视的出现，产生了彩色副载波信号来承载彩色信息。该信号成为同步发生器最重要的信号。在数字世界中，彩色副载波不再是视频信号的一部分。然而，它仍然用作同步发生器用于创建复合同步的基频。

As mentioned above, with the advent of color television, the color subcarrier signal was created to carry the color information. This signal became the most important signal of the sync generator. In the digital world, color subcarrier is no longer part of the video signal. However it is still used as the base frequency that a sync generator uses to create composite sync.

彩色副载波的频率为每秒 3,579,545 个周期。此频率必须保持在每秒正负 10 个周期内。如果这个频率发生变化，变化率不能大于每秒一个周期。该规范的准确性与人眼对颜色变化的敏感度有关。作为这种彩色副载波信号是颜色信息的参考，频率的任何变化都会导致颜色平衡发生变化。彩色副载波也用作整个视频信号的主要参考信号。如果彩色副载波不正确，那么电视系统中的所有信号都会受到影响。

The frequency of the color subcarrier is 3,579,545 cycles per second. This frequency must be maintained within plus or minus 10 cycles per second. If this frequency changes, the rate of change cannot be greater than one cycle per second every second. The exactness of this specification has to do with the sensitivity of the human eye to changes in color. As this color subcarrier signal was the reference for color information, any change in the frequency would cause a shift in the color balance. The color subcarrier is also used as the main reference signal for the entire video signal. If the color subcarrier is incorrect, then all the signals in the television system will be affected.

交叉脉冲显示

Cross Pulse Display

在专业视频监视器上，可以水平移动图像以使水平消隐期可见。图像也可以垂直移动以使垂直消隐间隔可见（图 4.2 (A)）。当图像同时水平和垂直移动时，显示称为交叉脉冲或脉冲交叉显示。交叉脉冲显示是在波形监视器上以电子方式表示的视觉图像。此显示显示了在同步发生器中创建的几个信号（图 4.2 (B)）。

On a professional video monitor, the image can be shifted horizontally to make the horizontal blanking period visible. The image can also be shifted vertically to make the vertical blanking interval visible (Figure 4.2 (A)). When the image is shifted both horizontally and vertically at the same time, the display is known as a cross pulse or pulse cross display. A cross pulse display is a visual image of what is represented electronically on a waveform monitor. This display shows several of the signals created in the sync generator (Figure 4.2 (B)).

其他信号输出

Other Signal Outputs

同步发生器通常提供测试信号，例如黑场和彩色副载波输出。其中一些输出可能会出现在面板的正面，以便于访问。这些相同的信号也可以在设备背面获得。其他测试信号将在本书后面讨论。

Sync generators often provide test signals, such as black burst and color subcarrier outputs. Some of these outputs may appear on the front of their face plates for ease of access. Those same signals are available at the back of the unit as well. Additional test signals are discussed later in the book.

垂直间隔信号

Vertical Interval Signals

NTSC模拟视频图像为525行，其中480行表示画面信息，简称活动视频。垂直间隔中的其余行用于同步信息。测试信号也被插入到垂直间隔中。虽然不是

The NTSC analog video image was 525 lines, 480 of which represent picture information, referred to as active video. The remaining lines in the vertical interval were used for synchronizing information. Test signals were inserted in the vertical interval as well. While not

图 4.2 A和B，模拟信号的交叉脉冲显示

Figure 4.2A and B, Cross Pulse Display of an Analog Signal

作为活动视频的一部分，它们是复合信号的重要组成部分。

part of the active video, they were a valuable part of the composite signal.

这些信号通常由连接到同步发生器的一个或多个输出的设备产生。然后可以将这些额外信号插入到垂直间隔中。这些信号包括垂直间隔测试信号、垂直间隔参考信号、隐藏式字幕、图文电视、商业插入数据和卫星数据。

These signals were usually created by devices connected to one or more of the outputs of a sync generator. These extra signals could then be inserted in the vertical interval. These signals included vertical interval test signals, vertical interval reference signals, closed captioning, teletext, commercial insertion data, and satellite data.

在垂直间隔测试信号 (VITS)的情况下，测试信号发生器可以创建多个测试信号的单行表示。这些单行测试信号被插入垂直间隔中未使用的视频行之一。VITS 可以显示在示波器上。该测试信号提供了关于帧中包含的活动视频的恒定参考。

In the case of the vertical interval test signals (VITS), a test signal generator could create one-line representations of several test signals. These one-line test signals were inserted in one of the unused video lines in the vertical interval. The VITS could be displayed on an oscilloscope. This test signal provided a constant reference with respect to the active video contained within the frame.

开发垂直间隔参考信号 (VIRS)以保持色彩保真度。当信号在设备之间切换时，颜色同步可能会出现细微差异。VIRS 为监视器或接收器提供了恒定的颜色参考。如果没有 VIRS，图像的色彩平衡可能会改变。

The vertical interval reference signal (VIRS) was developed to maintain color fidelity. Small differences in color synchronization can occur when signals are switched between pieces of equipment. The VIRS provided a constant color reference for the monitor or receiver. Without the VIRS, the color balance of the image might change.

隐藏式字幕最初是为了让听障人士可以观看节目并理解对话而开发的。在隐藏式字幕中，接收器从垂直间隔中获取信息并将其解码为活动视频中的字幕。隐藏式字幕也可用于音频可能不合适或不理想的环境中。从技术上讲，由于隐藏式字幕出现在第 21 行，这是活动视频，数据并不真正在垂直间隔中。

Closed captioning was originally developed so the hearing impaired could watch a program and understand the dialogue. In closed captioning, the receiver took the information from the vertical interval and decoded it into subtitles in the active video. Closed captioning could also be used in environments where the audio may not be appropriate or desired. Technically, since closed captioning appeared on line 21, which is active video, the data was not truly in the vertical interval.

商业广告插入数据可用于自动启动商业广告的播放。这可以消除的可能性操作员错误。数据旨在在适当的时间触发所需材料的回放，以及验证商业广告是否按订单播出。

Commercial insertion data can be used to automatically initiate the playback of a commercial. This can eliminate the possibility of operator error. The data are designed to trigger the playback of the required material at the appropriate time, as well as for verification that the commercial was broadcast as ordered.

卫星数据包含有关正在使用的卫星、卫星上的特定频道或转发器以及用于音频信号的频率的信息。

Satellite data contains information about the satellite being used, the specific channel or transponder on the satellite, and the frequencies used for the audio signals.

数字数据突发

Digital Data Bursts

图 4.3（图 1） 交叉脉冲显示中的数字数据突发

Figure 4.3 (Plate 1) Digital Data Bursts in a Cross Pulse Display

数字信号不需要消隐、垂直和水平同步信号。相反，每一行都有两个短数据突发，称为活动视频开始 (SAV) 和活动视频结束 (EAV)（图 4.3，图 1）。这使得模拟同步信号使用的信号流中的时间可用于其他用途。正是在这段时间内，音频信息（最多 16 个通道）和其他辅助数据信息是 插入。如果您检查数字信号的交叉脉冲显示，您可以看到在每条线之间的区域中形成的音频信息。这称为水平辅助数据区或 HANC。曾经插入模拟信号垂直间隔的信号类型现在承载在数字信号的垂直辅助数据区 (VANC) 中。

Digital signals do not require blanking, vertical and horizontal sync signals. Instead each line has two short data bursts called the Start of Active Video (SAV) and End of Active Video (EAV) (Figure 4.3, Plate 1). This leaves the time in the signal flow used by analog sync signals available for other uses. It is during this time that audio information (up to 16 channels) and other ancillary data information is inserted. If you examine the cross pulse display of a digital signal, you can see the audio information forming in the area between each line. This is called the horizontal ancillary data area, or HANC. The types of signals once inserted in the vertical interval of analog signals are now carried in the vertical ancillary data area (VANC) of the digital signal.

三电平同步

Tri-Level Sync

虽然 SAV 和 EAV 数据突发在数字信号内部工作以控制扫描和成帧，但仍然需要有一个信号可用于同步必须作为系统工作的设备。

While the SAV and EAV data bursts work inside the digital signal to control scanning and framing, there still needs to be a signal that can be used to synchronize devices that must work as a system.

随着 HDTV 的发展，匹配的模拟同步信号被创建来驱动现在已经过时的 HD 模拟版本的扫描。该信号称为三电平同步。它是传统同步的改进，现在通常称为双层同步以区别于较新的形式。大多数数字高清设备都可以使用任一类型的同步，并且大多数电视设施仍然在大多数情况下使用双电平形式。一些高清设备可能不接受双电平，因此您会在同步发生器和传统同步输出上找到三电平同步输出。

As HDTV was developed, a matching analog sync signal was created to drive the scanning of the now obsolete analog version of HD. This signal is called tri-level sync. It is a modification of traditional sync, which is now often call bi-level snyc to differentiate it from the newer form. Most digital HD equipment will work with either type of sync, and most TV facilities still use the bi-level form for most purposes. Some HD equipment may not accept bi-level, so you will find tri-level sync outputs on sync generators as well as traditional sync outputs.

总之，视频信号的水平和垂直消隐部分都承载着关键信息。除了同步之外，消隐期还用于携带其他数据，以提高视频信号的质量和实用性。

In summary, the blanking portions of the video signal, both horizontal and vertical, carry critical information. In addition to synchronizing, the blanking periods are used to carry other data that enhance the quality and usefulness of the video signal.

调制信号

Modulating the Signal

为了将此信息放在载体上，使用了称为调制的过程。调制意味着做出改变。在音乐中，改变音调被称为调制到不同的音调。歌曲的旋律和和声听起来是一样的，但是音调或音调是更低或更高。在广播中，对载波进行这种更改称为调制载波。

To put this information on the carrier, a process called modulation is used. To modulate means to make a change. In music, changing key is referred to as modulating to a different key. The melody and harmony of the song sound the same, but the key or pitch is lower or higher. In broadcasting, making this change to the carrier is called modulating the carrier.

图 5.1 载波和频率

Figure 5.1 Carriers and Frequencies

调制载波的方法有很多种。在模拟传输中，一种方法是改变施加在载波上的信号的高度或幅度。另一种方法是在载体上施加速度或频率不同的信号。将载波想象成前往目的地的旅程，将载波的调制想象成乘客。振幅变化或调制称为 AM，频率调制称为 FM（图 5.1）。在模拟电视广播中，视频图像 是通过载波的幅度调制传输的。信号的音频部分通过载波的频率调制传输。

There are many ways to modulate a carrier. In analog transmission one way is to change the height or amplitude of signals that are imposed on the carrier. Another way is to impose signals on the carrier that vary in speed or frequency. Think of the carrier wave as being the ride to the destination and the modulation of the carrier as the passenger. The amplitude change or modulation is referred to as AM, and the frequency modulation is referred to as FM (Figure 5.1). In analog television broadcasting, the video image was transmitted by amplitude modulation of the carrier. The audio portion of the signal was transmitted by frequency modulation of the carrier.

在视频捕捉链的开始，光线在相机中被转换成不同的电压。然后使用这些电压变化来改变载波的幅度。这些幅度变化与来自目标表面光的原始图像电压成正比。

At the beginning of the video capture chain, light is converted into varying voltages in the camera. These voltage variations are then used to make changes in amplitude on the carrier wave. These changes in amplitude were proportional to the original picture voltage which came from the light on the face of the target.

监视器或接收器要显示原始图像，必须首先接收载体。当接收器调谐到特定频道时，它对该载波的频率变得敏感。接收器通过解调过程，从载波上获取变化的幅度变化，并将该信息转换回与载波上的幅度变化成比例的变化电压。

For a monitor or receiver to show the original image, it must first receive the carrier. When a receiver is tuned to a specific channel, it becomes sensitive to the frequency of that carrier wave. The receiver, through the process of demodulation, takes the varying amplitude changes off the carrier and converts that information back to varying voltages proportional to the amplitude changes on the carrier.

在电视的接收器中，这个过程是相反的。变化的电压电平由监视器转换为光。这将整个过程带回到最初构成相机中图片的不同光照水平。

In the TV’s receiver, the process is reversed. The varying voltage levels are converted to light by the monitor. This brings the process full circle back to the varying light levels that originally made up the picture in the camera.

除了主要的视频载体之外，还有另外两个载体发送有关信号的音频和颜色部分的信息。这三个调制载波——一个用于视频，一个用于彩色副载波，一个用于音频——构成了总的复合信号。

In addition to the main video carrier, there were two other carriers that sent out information about the audio and the color portion of the signal. These three modulated carriers—one for video, one for color subcarrier, and one for audio—made up the total composite signal.

频谱

Frequency Spectrum

在自然界中，频谱的范围从零到无穷大。频谱以每秒周期数或赫兹 (Hz)的形式表示，以纪念科学家海因里希·赫兹 (Heinrich Hertz) 的名字命名，海因里希·赫兹 (Heinrich Hertz) 曾做过许多早期的磁学和电学实验。

In nature, the spectrum of frequencies ranges from zero to infinity. The spectrum is referred to in terms of cycles per second, or hertz (Hz), named in honor of the scientist Heinrich Hertz, who did many early experiments with magnetism and electricity.

人类体验的五种感觉中的三种——听觉、视觉和触觉——对频谱敏感。例如，耳朵能够听到 20 到 20,000 Hz 或 20 kHz（千赫兹）之间的声音。人类通常无法听到 20 kHz 以上的声音。在极高的频率下，我们的眼睛对光谱的特定部分变得敏感，并且能够看到光和颜色。频率在 432 万亿赫兹到 732 万亿赫兹之间的光变得可见。低于 432 万亿赫兹的频率称为红外线。红外线频率可以感觉到热量，但人眼看不到。高于 732 万亿赫兹的频率称为紫外线. 暴露在紫外线下的皮肤会受损，视力也会受损。在没有工具帮助的情况下，人类感觉只能直接感知总频谱中的一小部分（图 5.2，图 2）。

Three of the five senses human beings experience—hearing, seeing, and touch—are sensitive to the frequency spectrum. For example, the ear is capable of hearing between 20 and 20,000 Hz, or 20 kHz (kilohertz). Human beings are generally unable to hear sounds above 20 kHz. At extremely high frequencies, our eyes become sensitive to a certain portion of the spectrum and are able to see light and color. Light with frequencies between 432 trillion hertz and 732 trillion hertz becomes visible. Frequencies below 432 trillion hertz are called infrared. Infrared frequencies can be felt as heat, but cannot be seen by the human eye. Frequencies above 732 trillion hertz are called ultraviolet. Skin exposed to ultraviolet light can become damaged, as can one’s eyesight. Only a small portion of the total spectrum is directly perceptible to human sensation without the aid of tools (Figure 5.2, Plate 2).

图 5.2（图 2） 光谱

Figure 5.2 (Plate 2) Light Spectrum

模拟和数字广播

Analog and Digital Broadcasting

在美国，2009 年 6 月 12 日，所有主要电视台都关闭了模拟发射机。从那天起，FCC 强制要求对电视信号进行数字传输。一些低功率电台被允许继续播出几年。计划是在 2015 年关闭它们。

In the United States, on June 12, 2009, all major television stations shut off their analog transmitters. From that day on, the FCC mandated digital transmission of television signals. Some low power stations were allowed to remain on the air for a few years. The plan was to have them shut down in 2015.

频谱分为多个部分，其中一些部分已被命名，包括低频 (LF)、中频 (IF)、射频 (RF)、甚高频 (VHF) 和超高频 (UHF)。部分 VHF 和 UHF 频谱空间已分配用于模拟电视广播。1 到 13 之间的电视频道在 VHF 范围内。频道 14 到频道 59 在 UHF 范围内。通道 1 未使用，仅使用通道 2 至 59（图 5.3）。

The frequency spectrum is divided into sections, some of which have been given names, including low frequency (LF), intermediate frequency (IF), radio frequency (RF), very high frequency (VHF), and ultra high frequency (UHF). Portions of the VHF and UHF spectrum space have been allocated for use in analog television broadcasting. Television channels between 1 and 13 are in the VHF range. Channels 14 through channel 59 are in the UHF range. Channel 1 is not used, only channels 2 through 59 (Figure 5.3).

某些模拟电视频道之间的频谱分离比其他频道更大。例如，在一个有2频道的城市，不可能有3频道，因为这两个频道之间的间隔太窄，信号会相互干扰。然而，在有频道 4 的城市中，也可以有频道 5。这是因为这两个频道之间的频谱分离为每个频道提供了足够的空间来传输而不会相互干扰。

Certain analog television channels had a greater separation in the spectrum between them than others. For example, in a city where there is a channel 2, there could not be a channel 3, because the separation between these two channels was too narrow and the signals would interfere with each other. However, in a city where there is a channel 4, there can also be a channel 5. This is because the separation in the spectrum between these two channels allowed enough room for each to transmit without interference from the other.

这种额外的分离是因为所有电视频道都不在连续频率上。相反，其他服务出现在某些电视频道之间。例如，在频道 4 和 5 之间分配给航空导航系统，一个频段分配给射电天文学以及其他固定位置和移动无线电业务。

This additional separation is because all the TV channels are not on continuous frequencies. Instead other services appear between some TV channels. For example, between channels 4 and 5 are allocations for aviation navigation systems, a band for radio astronomy and other services for fixed position and mobile radio services.

图 5.3 频谱

Figure 5.3 Frequency spectrum

在从模拟广播到数字广播的转换中，为数字频道进行了新的频谱分配。相邻频道上的数字信号不会像模拟信号那样相互干扰。因此，电视频道可以彼此相邻，因此每个城市需要的频谱空间更少。FCC 重新分配了频道，使它们更紧密地组合在一起，并释放了频谱块用于其他用途。数字频道分配集中在频道 7–13、15–19、21–36 和 38–51 的原始频率上。在一些更拥挤的电视市场中，在可用的情况下使用额外的频率。

In the conversion from analog to digital broadcasting, new spectrum allocations were made for the digital channels. Digital signals on adjacent channels do not interfere with each other the way analog signals did. As a result, TV channels can be next to each other, so less spectrum space is needed in each city. The FCC reassigned channels to pack them closer together and free blocks of spectrum for other uses. The digital channel assignments are focused on the original frequencies for channels 7–13, 15–19, 21–36, and 38–51. In some of the more crowded television markets, additional frequencies are being used where available.

以这种方式压缩频道意味着大多数电台将不再具有相同的频道编号，因为它们分配的频率会随着数字广播而改变。电台所有者非常担心他们的观众无法找到新频道，他们几代人都知道在特定频道号码上寻找他们的节目。

Compacting the channels in this manner meant that most stations would no longer have the same channel number as their assigned frequency would change with digital broadcasting. Station owners were very concerned that their viewers, who for generations knew to look for their programs on a specific channel number, would not be able to find the new channel.

为了减少消费者的困惑，开发了虚拟渠道。虚拟频道是不同于实际分配的频道频率的频道名称。因此，想要收看他们所知道的第 7 频道的消费者可以将他们的电视调到该虚拟号码，但电视实际上设置为模拟频道 7 占用的不同频率。

To create less confusion for consumers, virtual channels were developed. A virtual channel is a channel designation that differs from the actual assigned channel frequency. So consumers who want what they know as channel 7 can tune their TV to that virtual number, but the TV is actually set to a different frequency occupied by the analog channel 7.

由于可以压缩数字信号以将比模拟信号更多的信息放入频谱空间，因此多个信号可以通过称为子频道。如果一个电台选择在其频道中播放多个节目，则每个节目流都会分配一个带小数点的数字。因此，如果频道 7 上有三个节目，当您调谐频道时，您将看到 7.1、7.2 和 7.3。请注意，这些数字仅出现在无线广播中。承载本地频道的有线和卫星运营商将在其频道地图中为附加节目分配不同的号码。

Because digital signals can be compressed to fit more information into the spectrum space than analog, multiple signals can be carried simultaneously in the same bandwith through what are called sub-channels. If a station chooses to carry multiple programs in their channel, each program stream is assigned a number with a decimal point. So if there are three programs on channel 7, as you tune up the channels you will see 7.1, 7.2 and 7.3. Note that these numbers only appear in the over the air broadcast. Cable and satellite operators that carry the local channel will assign different numbers in their channel map to the additional programs.

有线系统可以承载比广播更多的频道，因为有线信号不占用广播频谱空间。这些频率可以与其他广播服务（例如无线电、航空、军事和公共服务）使用的频率重叠，只要电缆本身得到适当屏蔽，以免干扰这些其他服务。

Cable systems can carry many more channels than can be broadcast because the cable signal does not take up broadcast spectrum space. The frequencies can overlap those used by other broadcast services, such as radio, aviation, military and public service as long as the cable itself is properly shielded so that no interference with these other services occurs.

带宽

Bandwidth

最初创建电视系统时，为每个频道分配了一个载波频率。还决定为每个特定电台提供 6 MHz 的带宽或频谱空间，用于在载波上传输电视信号。信号有上半部分和下半部分，称为上边带和下边带。电视广播中的 6 MHz 带宽仅使用上边带进行传输。如果同时使用上边带和下边带，它们将占用 12 MHz 的空间。不使用下边带，并在传输前将其滤除。重新创建电视信号所需的所有信息都包含在上边带中。

When the television system was originally created, a carrier frequency was assigned for each channel. It was also decided that 6 MHz of bandwidth or spectrum space would be made available for the transmission of television signals on the carrier for each particular station. A signal has an upper and a lower half, referred to as the upper and lower side bands. The 6 MHz of bandwidth in television broadcasting uses the upper side band only for transmission. If both upper and lower side bands were used, they would take up 12 MHz of space. The lower side band is not used and is filtered off before transmission. All the information necessary for the re-creation of the television signal is contained in the upper side band.

电视信号的 6 MHz 带宽限制是开发场处理或隔行扫描处理的原因之一。一次传输所有 525 行信息将占用的带宽远远超过分配给每个电视台的 6 MHz。因此，决定一次只传输一个场，不仅是为了最大限度地减少闪烁，也是为了保护频谱空间。

This limitation of 6 MHz of bandwidth for a television signal is one of the reasons the field process, or interlaced scanning process, was developed. To transmit all 525 lines of information at once would take far more bandwidth than the 6 MHz allocated for each television station. Consequently it was decided, not only to minimize flicker, but also for the conservation of spectrum space, to transmit only one field at a time.

例如，信道 2 在 54 和 60 MHz 之间给出，因为 6 MHz 带宽扩展允许传输。在模拟电视中，视觉载波位于允许频谱低端以上 11/4 MHz 的位置。因此，通道 2 的指定载波为 55.25 MHz。

For example, channel 2 was given between 54 and 60 MHz as the 6 MHz bandwidth spread allowed for transmission. In analog television, the visual carrier was placed 11/4 MHz above the low end of the allowable spectrum. Thus channel 2’s assigned carrier was 55.25 MHz.

与视频分开的音频载波始终比指定的视频载波频率高 4 1/2 MHz。对于通道 2，这意味着音频载波为 59.75 MHz，在音频载波和允许的频谱空间的上端之间留有 1/4 MHz 的空间。电视信号中的第三种载波是彩色副载波，这在第 4 章中进行了讨论。. 当在电视机上选择广播频道时，接收器对分配给该频道的频谱中的特定载频变得敏感。然后电视机接收该载体及其上的信息。它剥离不必要的载波频率并解调载波上包含的信息，从而重建原始电视图像。

The audio carrier, which was separate from the video, was always 4 1/2 MHz above the assigned carrier frequency for video. For channel 2, this means the audio carrier was 59.75 MHz, allowing 1/4 MHz of room between the audio carrier and the upper end of the allowed spectrum space. The third carrier in the television signal was the color subcarrier, which was discussed in Chapter 4. When a broadcast channel is selected on a television set, the receiver becomes sensitive to the particular carrier frequency in the spectrum that is assigned to that channel. The television set then receives that carrier and the information that is on it. It strips off the carrier frequency as unnecessary and demodulates the information that was contained on the carrier, and thus recreates the original television image.

在美国，数字电视传输使用称为 8-VSB 的调制方案。8是指3位数字系统可以产生的符号数。VSB 是残余边带调制。与模拟对应物一样，一个边带被滤掉，只留下一小部分或残余边带。音频和视频被合并并调制一个比 6 MHz 信道低端高 0.31 MHz 的导频。

In the U.S., digital television transmission uses a modulation scheme called 8-VSB. The 8 refers to the number of symbols that can be produced by a 3 bit digital system. VSB is vestigial sideband modulation. Like the analog counterpart, one sideband is filtered away, leaving only a small fraction, or vestigial sideband. The audio and video are combined and modulate a pilot frequency that is .31 MHz above the lower end of the 6 MHz channel.

还有其他调制数字广播信号的方法，例如 CODFM 和 QAM。在欧洲使用 CODFM 代替 8-VSB。QAM 是数字有线系统通常以多种形式之一采用的标准。

There are other ways to modulate a digital broadcast signal, for example CODFM and QAM. CODFM is used in place of 8-VSB in Europe. QAM is a standard often employed in one of several forms by digital cable systems.

卫星

Satellites

电视信号被称为视线信号，因为它们不随地球的曲线弯曲。它们穿透大气层并继续进入太空。正因为如此，即使不是不可能，也很难在距传输源 80 英里以外的地方接收电视信号。由于高度在发送和接收电视信号方面起着如此重要的作用，因此山顶和高天线被用来提供尽可能大的距离地球。在卫星通信发展之前，获得更大的射程是不切实际的。

Television signals are referred to as line of sight signals because they do not bend with the curve of the earth. They penetrate through the atmosphere and continue into space. Because of this, getting television reception beyond 80 miles or so from its transmission source becomes difficult, if not impossible. Since height plays such a major factor in sending and receiving television signals, mountaintops and tall antennas are used to provide as much range as possible from the earth. It was impractical to get any greater range until the development of satellite communications.

卫星根据反弹原理运行，将信号从一个地方反弹到另一个地方。这个概念类似于台球游戏，球被故意从桌子的一侧倾斜，进入另一侧的洞中。从地球发射的卫星在大约 25,000 英里的高度被送入环绕赤道的轨道。这给了他们一个非常高的点，从中可以将信号反射到地球。它允许更大的地理覆盖范围并克服地平线曲线的问题。在大约 25,000 英里处，绕地球运行所需的时间与地球自转的速度相匹配。这些因素使卫星在地球上方同步或静止。

Satellites operate on the principle of rebound, bouncing a signal from one place to another. The concept is similar to the game of pool, where a ball is purposely banked off of one side of the table to go into a hole on the other. Satellites launched from the earth are put into orbit around the equator at an altitude of about 25,000 miles. This gives them a very high point from which to bounce signals to the earth. It allows greater geographic coverage and overcomes the problem of the curve of the horizon. At about 25,000 miles, the time it takes to orbit the earth matches the speed that the planet spins. These factors make the satellite geosynchronous, or stationary, above the earth.

卫星在其使用寿命期间（通常约为十年）似乎会停留在天空中的固定位置。此时，太阳能电池开始显示其年龄，卫星耗尽了在其生命周期内进行轨道调整所需的燃料。

A satellite will appear to stay in a fixed position in the sky for the duration of its lifespan, which is typically about ten years. At this point, solar cells begin to show their age, and satellites run out of the fuel necessary to make orbital adjustments during their lifetime.

卫星在赤道周围的特定度数点进入轨道。沿赤道弧的轨道空间由国际协议分配，类似于广播频率中的频谱空间。北美大陆，包括美国、加拿大和墨西哥，西经大约为 67º 至 143º。早期的卫星围绕赤道间隔 4º 放置，每颗卫星有多达 12 个转发器，或可用的沟通渠道。随着天线和电子设备技术的改进，赤道弧上的间距已减小到不到 1º。每一代新卫星都会增加可用转发器的数量。目前可以有 50 多个。而且，数字压缩允许每个转发器携带一个以上的信号。根据从卫星供应商处购买的带宽，每个转发器可以处理大约 10 个不同的视频信号。

Satellites are placed into orbit at specific degree points around the equator. The orbital space along the equatorial arc is assigned by international agreement, similar to the spectrum space in broadcast frequencies. The North American continent, including the U.S., Canada, and Mexico, has from approximately 67º to 143º west longitude. The early satellites were placed 4º apart around the equator, and each satellite had as many as 12 transponders, or channels of communication available. With improvements in the technology of both the antennas and the electronics, spacing has been reduced to less than 1º in the equatorial arc. Each new generation of satellite increases the number of transponders available. Currently there can be more than 50. Also, digital compression allows each transponder to carry more than one signal. Depending on the bandwidth purchased from the satellite vendor, about 10 different video signals can be handled by each transponder.

上行链路和下行链路

Uplink and Downlink

卫星信号覆盖的地球区域称为足迹。足迹的大小可以随卫星运营商的意愿而变大或变小。对于美国大陆的一般电视用途，足迹覆盖整个国家。在欧洲，足迹可以限制在一个国家或允许覆盖整个大陆（图 5.4）。

The area of the earth that the satellite signal covers is known as the footprint. The size of the footprint can be as large or as confined as the operator of the satellite wishes. For general television purposes in the continental United States, the footprint covers the entire country. In Europe, footprints can be confined to a single country or allowed to cover the entire continent (Figure 5.4).

有时，当需要长距离传输时，可能会使用两颗卫星，即所谓的双跳。例如，在 从洛杉矶到巴黎的双跳，信号将被传输到北美上空的卫星，并在例如纽约市或蒙特利尔的下行链路设施接收。然后，该设施会将信号上传到大西洋上空的卫星。然后，巴黎的下行链路设施将接收到该信号。

On occasion, when long-distance transmission is required, two satellites may be used in what is called a double hop. For example, in a double hop from Los Angeles to Paris, the signal would be transmitted to a satellite over North America and received at a downlink facility in, for instance, New York City or Montreal. This facility would then uplink the signal to a satellite over the Atlantic Ocean. The signal would then be received at a downlink facility in Paris.

图 5.4 卫星足迹

Figure 5.4 Satellite Footprint

在为上行链路或下行链路设置碟形卫星天线时，需要对准三个位置。第一个是天线设置在地球上方的仰角或角度。第二个是天线指向的度数或罗盘航向。第三是天线的极性，或水平或垂直排列。这三个规格允许天线指向天空中的确切位置以找到信号。这些比对的准确性至关重要。

In setting the antenna of a satellite dish for either an uplink or downlink, there are three positions to align. The first is the elevation or angle above the earth at which the antenna is set. The second is the degree or compass heading toward which the antenna is pointing. The third is the polarity, or horizontal or vertical alignment, of the antenna. These three specifications allow the antenna to be pointed at an exact place in the sky to find the signal. The exactness of these alignments is critical.

如果这些测量值中的任何一个不正确，则信号可能会被分配给不同上行链路设施的卫星或转发器接收。结果是两个图像在指定用于接收图像的下行链路设施处相互叠加。这称为双重照明。接收到的两个信号同一颗卫星上的同一个转发器同时使两个图像都无用。如果碟形卫星天线在下行链路或接收时未对准，接收到的图像质量将受到影响。

If any of these measurements are incorrect, it is possible that the signal will be received by a satellite or transponder assigned to a different uplink facility. The result is two images superimposed on each other at the downlink facilities assigned to receive the images. This is referred to as double illumination. Two signals received by the same transponder on the same satellite at the same time renders both images useless. If the satellite dish is misaligned for the downlink or reception, the quality of the image that is received will be compromised.

接收信号或向卫星传输信号的抛物面天线的大小也是区分各种卫星和转发器的能力的一个因素。出于传输目的，法律规定了最小天线尺寸。此要求是为了确保传输的信号到达其特定目标或卫星。接收盘可以是任何尺寸，但接收盘越大，接收效果越好。

The size of the parabolic dish that receives or transmits a signal to a satellite also plays a factor in the ability to discriminate between the various satellites and transponders. For transmission purposes, the law requires a minimum dish size. This requirement is to assure the transmitted signal reaches its specific target, or satellite. The receiver dish can be any size, but the larger the dish, the better the reception.

卫星信号以光速传播。实际行驶的距离约为往返 45,000 英里。由于这个距离，从传输到接收大约有四分之一秒的延迟。

Satellite signals travel at the speed of light. The actual distance traveled is almost 45,000 miles round-trip. Because of this distance, there is a delay of about a quarter of a second from transmission to reception.

光纤

Fiber Optics

使用光来传输信息是一种可以追溯到几千年前的非常古老的通信方式。灯笼灯或信号火是原始形式。原始电话的发明者亚历山大·格雷厄姆·贝尔 (Alexander Graham Bell) 是使用光来传输人类语音的早期现代开发人员之一。他发明了一种他称之为“光电电话”的设备。贝尔利用阳光反射到因人声而振动的膜上。反射的阳光脉冲被位于一定距离外的抛物面接收。光脉冲在接收端放置在盘子中间的硒电池中产生电波动。该电池连接到耳机和电池。细胞产生电流波动，振动耳机中的薄膜并重现声音。

Using light to transmit information is a very old form of communication going back thousands of years. Lantern light or signal fires were the original forms. Alexander Graham Bell, the inventor of the original telephone, was one of the early modern developers who used light to transmit human speech. He invented a device he called the “photophone.” Bell used sunlight reflected against a membrane that vibrated from the sound of a human voice. The reflected sunlight pulses were received by a parabolic dish located some distance away. The light pulses generated electrical fluctuations in a selenium cell placed in the middle of the dish on the receiving end. This cell was attached to earphones and a battery. The cell created electrical current fluctuations that vibrated the membrane in the earphones and recreated the voice.

图 5.5（图 3） 光纤电缆

Figure 5.5 (Plate 3) Fiber Optic Cable

1934 年开发了使用玻璃纤维进行光传输的系统，该系统使用光通过光缆网络传输人声。光纤的最新发展现在允许以非常高的速度传输非常大量的数据。现在可以传输的数据的速度和数量是光学纯玻璃、LED（发光二极管）和激光（通过受激辐射的光放大）的发展的函数（图 5.5，图3） .

The use of glass fiber for light transmission was developed in 1934 with a system that used light to transmit the human voice over an optical cable network. Recent developments in fiber optics now allow the transmission of very large quantities of data at very high rates of speed. The speed and quantity of the data that can now be transmitted are a function of the development of optically pure glass, LEDs (light-emitting diodes), and the LASER (Light Amplification through Stimulated Emission of Radiation) (Figure 5.5, Plate 3).

当光穿过玻璃纤维时，必须使用光学纯玻璃来最大程度地减少信号强度的损失。光学纯玻璃非常透明，如果将其堆叠超过一英里，您可以清楚地看到底部。

Optically pure glass is necessary to minimize the loss of signal strength when the light moves through the glass fiber. Optically pure glass is so clear that if more than a mile of it were stacked up, you could see through to the bottom clearly.

在光纤网络中使用激光和 LED 生成光脉冲既有优点也有缺点。

There are advantages and disadvantages to the use of lasers and LEDs in generating the light pulses used in a fiber optic network.

激光更强大，并以最适合在光纤网络中使用的频率发射光。所需的特定频率由三件事决定：(1) 传输的数据类型，(2) 需要最小化通过光纤时的光损失，以及 (3) 传输数据所需的距离。然而，激光器价格昂贵、需要维护、对环境敏感并且比 LED 老化得更快。它们还需要定期重建或更换。

The laser is more powerful and emits light at the frequencies that are optimal for use in a fiber network. The specific frequencies needed are dictated by three things: (1) the types of data being transmitted, (2) the need to minimize light loss when going through the fiber, and (3) the distance needed to transmit the data. However, lasers are expensive, require maintenance, are environmentally sensitive, and age more rapidly than LEDs. They also require periodic rebuilding or replacement.

LED 制造起来更简单、更便宜，使用寿命比激光更长，而且不像激光那样对环境敏感。然而，它们的功率低于激光，并且不能很好地远距离传输。因此，激光倾向于用于长距离传输，如跨国或洲际使用；LED 通常用于较短的距离，例如局域网 (LAN) 或光纤分布式数据接口 (FDDI) 应用，例如位置较近的建筑物或设施内或之间。

LEDs are simpler and cheaper to manufacture, last longer than lasers, and are not as environmentally sensitive as lasers. However, they are lower in power than lasers and do not transmit well over long distances. Therefore, lasers tend to be used for long-distance transmission such as cross-country or intercontinental use; LEDs typically are used for shorter distances such as in local area network (LAN) or Fiber-Distributed Data Interface (FDDI) applications, such as within or between closely situated buildings or facilities.

由于数字数据由零和一组成，因此将数据转换为光脉冲并不困难。那些由光脉冲表示，零由没有光脉冲表示。这类似于同样使用激光的 CD 和 DVD 刻录。然而，在那些情况下，激光用于刻蚀磁盘记录表面上的凹坑、谷底或平坦区域。使用光纤传输系统，数据从一端发送到另一端，但不存储在光纤线路中。光纤只是发送和接收数据的一种手段，一种光导。

As digital data consists of zeros and ones, converting the data to light pulses is not difficult. The ones are represented by pulses of light and zeros are represented by the absence of a light pulse. This is similar to CD and DVD recordings that also use a laser. However, the laser in those instances is used to burn pits, valleys, or flat areas on the recording surface of the disk. With a fiber optic transmission system, the data is sent from one end to the other but not stored in the fiber lines. The fiber is only a means of sending and receiving data, a light guide.

光纤传输的工作原理

How Fiber Optic Transmission Works

光纤传输通过将电能转换为光脉冲来发挥作用。这些光脉冲通过玻璃纤维发送。在接收端，光脉冲被转换为电由称为光学检测器的设备发出脉冲。有多种光学检测器，例如光电二极管、PIN 二极管和雪崩光电二极管。选择使用哪一个取决于传输系统和网络建设本身。检测器将光脉冲转换为电能，然后用于在电子设备中重建数据。

Fiber optic transmission functions by converting electrical energy to pulses of light. These light pulses are sent through the glass fiber. On the receiving end, the light pulses are converted to electrical pulses by a device called an optical detector. There are several varieties of optical detectors such as photodiodes, PIN diodes, and avalanche photodiodes. The choice of which one to use is dictated by the transmitting system and the network construction itself. The detector converts the light pulses to electrical energy, which is then used to recreate the data in an electronic device.

光纤有三种模式：单模光纤、多模光纤和塑料光纤（POF）。

There are three modes of fiber optics: single-mode fibers, multimode fibers, and plastic optical fiber (POF).

单模光纤电缆仅使用一种模式的光通过光纤电缆传输数据。在这种情况下，模式一词指的是光在光纤内通过或传播的方式。在单一模式下，所有光线的行为都相同。

Single-mode fiber optic cable uses only one mode of light to transmit the data through the fiber optic cable. In this instance the word mode refers to the way the light passes or prorogates inside the fiber. With single mode all the light behaves the same way.

多个串行数字数据流可以组合在一起并通过单模光纤同时传输。此过程称为多路复用。多路复用利用数据包之间出现的空间来插入额外的数据。这样，许多数据流可以交织在一起并同时发送。

Multiple streams of serial digital data can be grouped together and transmitted simultaneously through the single-mode fiber. This process is known as multiplexing. Multiplexing exploits the spaces that occur between packets of data to insert additional data. In this way, many data streams can be interwoven and sent simultaneously.

单股单模光纤的直径在 8 到 10 微米之间。一微米是一米的百万分之一。许多光纤束可以捆绑在一起以增加已安装系统的数据容量。

A single strand of single-mode fiber measures between eight and ten microns in diameter. A micron is one-millionth of a meter. Many strands of fiber may be bundled together to increase the data capacity of an installed system.

多模光纤电缆使用多种模式的传播光来传输数据（图 5.6）。因为多模光纤的纤芯比单模光纤粗得多，所以当光在内部反射时，一部分光会经过更长的路径到达另一端。随着光的传播，波分为多种传播“模式”。多模光纤比单模光纤能够承载更多的数据。多模光纤束在 50 根之间测量 直径一百微米。这些也可以捆绑在一起以增加网络的容量。

Multimode fiber optic cable uses multiple modes of propagation light to carry data (Figure 5.6). Because the core of multimode fiber is much thicker than single mode, as the light is reflected internally some part of the light takes a longer path to the other end. As the light spreads out the waves break into multiple “modes” of propagation. Multimode fibers are capable of carrying more data than single-mode fibers. Multimode fiber strands measure between fifty and one hundred microns in diameter. These can also be bundled together to increase the capacity of the network.

图 5.6 多模光纤

Figure 5.6 Multimode Fiber Optics

塑料光纤是一种较便宜的光缆。您可能熟悉这种塑料电缆，因为它以名称 TOSLINK 用于消费类音频应用。通过光纤连接，单根电缆可以承载多个音频通道，就像您在环绕声系统中发现的那样。由于光在塑料电缆中比在玻璃中衰减得更快，因此这些电缆的长度限制在几米以内。

Plastic optical fiber is a less expensive form of fiber optic cable. You may be familiar with this plastic cable as it is used in consumer audio applications under the name TOSLINK. With fiber connections, a single cable can carry multiple channels of audio as you might find with surround sound systems. Because the light is attenuated more rapidly in plastic cable than in glass, these cables are limited to a few meters in length.

在需要重新放大光脉冲以继续传输之前，单模光纤能够传输长达 5 公里（约 3 英里）的数字数据。在必须重新放大光脉冲之前，多模光纤能够传输长达 3 公里（或大约 1.8 英里）的数字数据。这个范围比铜线的等效范围大得多，因此在构建数据网络的总成本方面更便宜。

Single-mode fiber is capable of carrying digital data up to 5 kilometers, or about 3 miles, before the light pulses need to be reamplified to continue transmission. Multimode fiber is capable of carrying digital data up to 3 kilometers, or approximately 1.8 miles, before the light pulses must be reamplified. This range is considerably greater than the equivalent in copper wire and therefore less expensive in the overall cost of constructing a data network.

光缆本身由多层材料制成。电缆的核心是以微米为单位的玻璃纤维。玻璃然后在光纤上涂上一层包层，这是一种光反射材料，可将光线限制在玻璃纤维内。包层周围是一层塑料缓冲涂层，可保护包层和玻璃纤维，有助于吸收物理冲击，并防止过度弯曲。塑料涂层周围是强化纤维，可以是织物（如凯夫拉尔或芳纶）、线束，甚至是凝胶填充套管。所有这些周围都是外层，一般来说，每根电缆都有 PVC 塑料，用于保护电缆并印有制造商信息。

The fiber optic cable itself is made of several layers of material. The core of the cable is the glass fiber measured in microns. The glass fiber is then coated with a cladding, which is a light reflective material that keeps the light confined within the glass fiber. Surrounding the cladding is a layer of a plastic buffer coating that protects the cladding and glass fiber, helps to absorb physical shocks, and protects against excessive bending. Surrounding the plastic coating are strengthening fibers that can be fabric (such as Kevlar or Aramid), wire strands, or even gel-filled sleeves. Surrounding all of this is the outer layer of, generally, PVC plastic that every cable has that protects the cable and has the manufacturer’s information printed on it.

与铜缆相比，光纤电缆具有许多优势：它可以在更长的距离内传输更多的数据；携带的数据不受电磁干扰；而且电缆的重量比传统的铜电缆轻得多。这些都是网络和设施建设的重要考虑因素。

Fiber optic cable has many advantages over copper: It will carry considerably more data over much longer distances; the data carried is immune to electro-magnetic interference; and the cable is much lighter in weight than conventional copper cables. These are strong considerations in network and facility construction.

光纤也有一定的缺点，成本是其中之一。光纤网络的初始成本高于使用传统的铜缆。玻璃纤维也比较脆弱；它很容易被打破。虽然光纤具有很大的抗拉强度，因此可以像铜线一样通过拉动光缆来完成安装，但它对可能破坏玻璃光纤的弯曲和挤压力有非常严格的限制。光缆的拼接和连接非常精确，安装连接器和进行拼接所需的设备价格昂贵，而且其精度比同等的铜缆安装设备更为关键。

Fiber optics also has certain disadvantages, cost being one of them. The initial cost of a fiber network is more than using conventional copper cables. Glass fiber is also more fragile; it can be broken easily. Though fiber has great tensile strength, and so installation can be accomplished by pulling the fiber cable in the same manner as copper lines, it has very strict limitations on bends and crushing forces that can destroy the glass fiber. Splicing and connecting fiber cables is very exact, and the equipment needed to install connectors and make splices is expensive and more critical in its precision than the equivalent copper installation equipment.

目前，光纤电缆主要用于需要大量数据传输的公司，例如电视设施和电话公司。然而，有一种在所谓的光纤到户 (FTTH) 中为消费者安装光纤的举措。因为这很昂贵，而且现有系统的限制还没有达到或超过，所以 FTTH 是一个持续的企业。

Currently, fiber optic cables are primarily used by companies such as television facilities and telephone companies that require heavy data transmission. However, there is a move to install fiber to consumers in what is called Fiber To The Home (FTTH). As this is expensive and the limits of the existing system have not been reached or exceeded, FTTH is an on-going enterprise.

加法和减法

Additive and Subtractive

感知颜色有两种方式。一种方法是将光的频率加在一起，这被称为加色系统。任何发光系统，例如电视监视器，都是附加的。在加色环境中，所有原色的组合产生白光。阳光是所有颜色的组合，具有叠加性。

There are two ways that color is perceived. One way is by adding the frequencies of light together, which is referred to as the additive color system. Any light-emitting system, such as a television monitor, is additive. In an additive environment, the combination of all the primary colors yields white light. Sunlight, which is a combination of all the colors, is additive.

相反，包括印刷媒体在内的固体物体不会发光，而是通过减色过程被感知。也就是说，物体吸收物体不吸收的每一种颜色频率。除看到的颜色外，所有颜色都被减去，这些颜色被反射。因此，固体物体的颜色是它反射的光。在减色系统中，所有颜色加在一起产生黑色。这是因为所有频率都被物体吸收而没有被反射。

Conversely, solid objects, including print media, do not emit light and are perceived through a subtractive process. That is, the objects absorb every color frequency that the object is not. All colors are subtracted except the ones seen, which are reflected. Therefore, the color of a solid object is the light reflected by it. In a subtractive color system, all of the colors added together yield black. This is because all the frequencies are absorbed by the object and none are reflected.

原色和副色

Primary and Secondary Colors

在任何颜色系统中，某些颜色被称为原色。原色的定义是它不能通过任何其他原色的组合来创建。例如，在红绿蓝（RGB）颜色系统中，红色不能由蓝色和绿色组合产生，绿色不能由红色和蓝色组合产生，蓝色不能由红色和绿色组合产生。在定义颜色系统时，任何一组颜色都可以用作原色。原色系统可以包括三种以上的原色。同样，必须遵守的唯一规则是任何两种原色的组合不能创建其他原色之一。

In any color system, certain colors are referred to as primary. The definition of a primary color is that it cannot be created through a combination of any of the other primary colors. For example, in a red, green, and blue (RGB) color system, red cannot be created by combining blue and green, green cannot be created by combining red and blue, and blue cannot be created by combining red and green. When defining a color system, any set of colors can be used as the primaries. A primary color system can include more than three primary colors. Again, the only rule that must be adhered to is that the combination of any two of the primary colors cannot create one of the other primaries.

电视中的基本色彩系统是三原色加色系统。电视中的原色是红色、绿色和蓝色 (RGB)。结合两种原色会产生二次色。结合二次色创建三次色。在彩色电视系统中，有黄色、青色和品红色三种二次色，它们分别是两种原色的组合。黄色是红色和绿色的组合，青色是绿色和蓝色的组合，品红色是红色和蓝色的组合（图 6.1，图 4）。

The basic color system in television is a three primary color additive system. The primary colors in television are red, green, and blue (RGB). Combining two primary colors creates a secondary color. Combining secondary colors creates a tertiary color. In the color television system, there are three secondary colors—yellow, cyan, and magenta—which are each combinations of two primary colors. Yellow is the combination of red and green, cyan is the combination of green and blue, and magenta is a combination of red and blue (Figure 6.1, Plate 4).

图 6.1（图 4） 原色和二次色

Figure 6.1 (Plate 4) Primary and Secondary Colors

颜色系统

The Color System

在 50 年代初期，NTSC（国家电视系统委员会）以及其他团体和个人致力于为电视信号添加色彩的目标。第一个开发的 NTSC 电视系统是黑白的，或单色的。NTSC 电视传输是在 6 MHz 左右的频谱空间中创建的，用于传输黑白图像和音频信号。

In the early 1950s, the NTSC (National Television System Committee), as well as other groups and individuals, worked toward the goal of adding color to the television signal. The first NTSC television systems that were developed were black and white, or monochrome. NTSC television transmission was created around 6 MHz of spectrum space for transmission of the black and white picture and audio signal.

NTSC 彩色的发展带来了一个问题，因为单色电视系统已经到位。将颜色信息添加到单色信号本来是一个非常简单的解决方案，但这样做会占用两倍的频谱空间。考虑到当时的系统，这是不可能的。此外，这种颜色系统与现有的黑白系统不兼容。添加颜色的技巧到现有的黑白载波上是在 6 MHz 带宽内添加它，从而保持兼容性。

The development of NTSC color posed a problem because the monochrome television system was already in place. Adding color information to the monochrome signal would have been an easy enough solution, but doing that would have taken up twice the amount of spectrum space. This wasn’t possible given the system in place at the time. Also, this color system would not have been compatible with the existing black and white system. The trick to adding color onto the existing black and white carrier was to add it within the 6 MHz of bandwidth, thus maintaining compatibility.

与电视中的许多挑战一样，部分解决方案是数字游戏。通过简单地使用数学并改变一些数字，可以在不改变其基本结构的情况下对系统进行更改。PAL 和 SECAM 系统是在 NTSC 彩色系统之后开发的。

As with many challenges in television, part of the solution was a game of numbers. By simply working with the mathematics and altering some of the numbers, changes in the system could be made without changing its basic structure. The PAL and SECAM systems were developed following the NTSC color system.

所有这三个系统——NTSC、PAL 和 SECAM——都是对颜色进行编码的模拟方法，以便可以广播颜色信号。然而，数字系统不需要创建复合信号，但它们仍然使用以下一些步骤来生成数字彩色信号。这些系统通常采用一些影响帧速率的技术，以提供与以模拟形式录制的大量节目库的兼容性。

All three systems—NTSC, PAL and SECAM—are analog methods of encoding color so that color signals could be broadcast. Digital systems, however, do not need to create a composite signal yet they still use some of the steps that follow to make digital color signals. These systems often honor some of the techniques that affect frame rate to provide compatibility with the vast libraries of shows recorded in analog form.

谐波

Harmonics

谐波和八度在创建模拟彩色视频的过程中起着重要作用。八度是频率的两倍。例如，在音乐中，音符“A”位于 440 赫兹。要听到比这高一个八度的另一个“A”，频率将加倍至 880 赫兹。高于 1,000 赫兹的八度将是 2,000 赫兹。2,000 以上的八度为 4,000；高于 4,000 的八度为 8,000；等等。

Harmonics and octaves play an important role in the process of creating analog color video. An octave is a doubling of a frequency. For example, in music, the tuning note “A” lies at 440 hertz. To hear another “A” an octave above this, the frequency would be doubled to 880 hertz. An octave above 1,000 hertz would be 2,000 hertz. An octave above 2,000 would be 4,000; an octave above 4,000 would be 8,000; and so on.

另一方面，谐波是通过再次将初始频率或基音添加到自身而不是加倍频率来改变的频率。例如，如果一次谐波或基音为 1,000 赫兹，则二次谐波为 2,000 赫兹，三次谐波为 3,000，四次谐波为 4,000，依此类推。

Harmonics, on the other hand, are frequencies that change by adding the initial frequency or fundamental tone to itself again, rather than doubling the frequency. For example, if the first harmonic or fundamental tone is 1,000 hertz, the second harmonic would be 2,000 hertz, the third harmonic 3,000, the fourth harmonic 4,000, and so on.

NTSC 单色电视线路频率为 15,750 赫兹。通过将 15,750 赫兹加到自身上可以找到该数字的谐波。二次谐波为 31,500 赫兹，三次谐波为 47,250 赫兹，依此类推。在电视中发现的是，在载波频率上调制的视频信息似乎围绕线路频率的谐波进行分组。这在载体上留下了很少或没有携带信息的地方。

The NTSC monochrome television line frequency was 15,750 hertz. Harmonics of that number can be found by adding 15,750 hertz to itself. The second harmonic would be 31,500 hertz, the third 47,250 hertz, and so on. What was discovered in television was that the video information modulated on the carrier frequency seemed to be grouping itself around the harmonics of the line frequency. That left places on the carrier where little or no information was being carried.

发现载体中的这些空间在数学上处于一半线路频率的奇次谐波处（图 6.2）。行频的一半是每秒 7,875 行。如果这是一次谐波，那么三次谐波将是 7,875 的 3 倍，即 23,625。五次谐波将是 7,875 或 39,375 的 5 倍，依此类推直至兆赫兹范围。

These spaces in the carrier were discovered to be mathematically at the odd harmonics of half of the line frequency (Figure 6.2). Half of the line frequency was 7,875 lines per second. If that is the first harmonic, then the third harmonic would be 3 times 7,875, or 23,625. The fifth harmonic would be 5 times 7,875, or 39,375, and so on up the scale into the megahertz range.

对载体的检查表明在这些频率上有可用空间。可以在这些空间中插入其他视频信息，而不会对正在广播的现有信息造成任何干扰。将这些空间用于颜色信息意味着现有的黑白系统和新的颜色系统可以兼容。

An examination of the carrier revealed that space was available at these frequencies. Other video information could be inserted in these spaces without causing any interference with the existing information being broadcast. Using these spaces for color information meant that the existing black and white system and the new color system could be compatible.

NTSC 彩色传输

NTSC Color Transmission

为了传输 NTSC 信号的彩色部分，需要一个额外的载波频率。这个想法是让新的载波频率尽可能高，因为更高频率的信号会产生更少的干扰，并且会在现有的黑白系统中导致更少的问题。因此将线路频率的一半的455次谐波设置为彩色副载波频率。之所以称为副载波，是因为它是主载波内的附加信息载体。

In order to transmit the color portion of the NTSC signal, an additional carrier frequency was needed. The idea was to make that new carrier frequency as high as possible, because higher frequency signals cause less interference and would result in fewer problems in the existing black and white system. So the 455th harmonic of half the line frequency was set as the color subcarrier frequency. It is called a subcarrier because it is an additional carrier of information within the main carrier.

图 6.2 奇次谐波

Figure 6.2 OddHarmonics

这本身就造成了另一个问题。所有电视台的所有音频载波都设置为比视频载波高 4.5 MHz。无论视频载波的频率如何，电视机都被制造成可以检测到高于该频率 4.5 MHz 的音频载波。人们发现，新的彩色副载波会导致音频载波在 900 千赫范围内的某处发生拍频或干扰。这在图片中可以看到波浪状的黑白线条。那么问题就变成了如何消除拍频及其可见干扰。

This in itself caused another problem. All audio carriers were set at 4.5 MHz above the video carrier for all television stations. Whatever the frequency of the video carrier, television sets were made so that they would detect the audio carrier at 4.5 MHz above that. It was discovered that the new color subcarrier caused a beat frequency, or interference, to occur with the audio carrier somewhere in the area of 900 kilohertz. This was visible as wavy black and white lines going through the picture. The problem then became how to eliminate that beat frequency and its visible interference.

由于所有电视机都在比视频载波高 4.5 MHz 的位置寻找音频载波，因此无法更改音频载波。同时，彩色副载波是从现有的线路频率中数学导出的，不能任意更改。

Since all television sets looked for the audio carrier at 4.5 MHz above the visual carrier, the audio carrier could not be changed. At the same time, the color subcarrier was derived mathematically from an already existing line frequency and could not be changed arbitrarily.

人们发现，通过将现有的每秒 15,750 线频率减慢到大约每秒 15,734 线频率，其中一半的 455 次谐波将是不会以可见方式干扰音频载波的彩色副载波频率。该彩色副载波恰好适合由线路频率的谐波创建的空间之一。

It was discovered that by slowing the existing line frequency of 15,750 lines per second to approximately 15,734 lines per second, the 455th harmonic of half of that would be a color subcarrier frequency that would not interfere with the audio carrier in a way that was visible. This color subcarrier fits properly in one of the spaces created by harmonics of the line frequency.

同时，这种新的行频比现有的黑白系统慢了 16 行，但仍然与现有的电视机兼容。电视设备设计为在大约 1% 的线路频率变化范围内工作。15,750 的百分之一大约是 157 行。由于新的线路频率仅降低了大约 16 条线路，因此在现有线路频率的 1% 的 1/10 以内。

At the same time, this new line frequency, which was essentially 16 lines slower than the existing black and white system, was still compatible with existing television sets. Television equipment was designed to work within a range of approximately 1% variation in line frequency. One percent of 15,750 is approximately 157 lines. As the new line frequency was only slowed down by approximately 16 lines, it was within 1/10 of 1% of the existing line frequency.

NTSC 彩色帧率

NTSC Color Frame Rate

当时的黑白电视机可以应对这种变化而不会显示任何干扰。稍慢的线路频率产生了每秒 29.97 帧的新帧速率。这意味着完成扫描完整 30 帧的时间略长于一秒。对于彩色电视，29.97 帧速率或 59.94 场速率不会锁定 60 周期电流或 AC（交流电）。因此，需要更改同步引用。因此，模拟电视系统参考了彩色副载波。

Black and white television sets of that time could handle this change and not display any interference. The slightly slower line frequency produced a new frame rate of 29.97 frames per second. This means that it took slightly longer than one second to complete scanning a full 30 frames. With color television, the 29.97 frame rate—or 59.94 field rate—does not lock with 60 cycle current, or AC (alternating current). Consequently, synchronizing references needed to change. Therefore, analog television systems were referenced to the color subcarrier.

开发数字电视时，保留了这种非整数帧速率，以便将遗留素材轻松集成到当前制作中。因此，这个解决 1950 年代模拟问题的方法在今天仍然存在于美国用于广播的帧速率中。如果您希望广播您的项目，最好使用 29.97 帧速率。

When digital television was developed, this non-integer frame rate was retained to make it easy to integrate legacy material in current productions. So this fix for a 1950’s analog problem lives on today in the frame rates used in the United States for broadcasting. If you anticipate broadcasting your projects, it is a good practice to use the 29.97 frame rate.

编码颜色信号

Encoding the Color Signal

不幸的是，载体上的可用空间无法容纳所有三种颜色（红色、绿色和蓝色信号）所需的信息。因此需要一种编码系统，以便将所有这些信息压缩到彩色副载波信号上。

Unfortunately, the information needed for all three colors (the red, green, and blue signals) would not fit in the available spaces on the carrier. So a system of encoding was needed in order to compress all of this information onto the color subcarrier signal.

对红色、绿色和蓝色信息进行编码的过程基于数学，在这种情况下，基于平面几何。在平面几何中，勾股定理指出直角三角形各边的平方和等于第三边的平方。这意味着如果知道直角三角形两条边的尺寸，就可以计算出第三条边。使用毕达哥拉斯定理，如果已知其中两种颜色的强度，则可以计算出第三种。红色和蓝色成为测量信号，绿色成为导出或计算值。

The process of encoding the red, green, and blue information is based on mathematics and, in this case, plane geometry. In plane geometry, the Pythagorean theorem states that the sum of the squares of the sides of a right triangle is equal to the square of the third side. That means that if the measurements of two sides of a right triangle are known, the third side can be calculated. Using the Pythagorean theorem, if the strength of two of the colors is known, the third can be calculated. Red and blue became the measured signals, and green the derived or calculated value.

载体

Vectors

图 6.3 矢量示波器上的颜色条

Figure 6.3 Color Bars on Vectorscope

彩色视频可以表示为矢量。矢量是特定方向上的力的数学表示。矢量的长度表示力的大小，矢量的方向是矢量相对于固定参考指向的方向，就像指南针一样。用于查看和测量这些矢量的设备称为矢量示波器（图 6.3）。喜欢 波形监视器、矢量示波器显示可视图像的电子表示。（矢量示波器在第 8 章中有更详细的讨论。）在电视中，矢量的方向决定了特定的颜色，而长度代表了该颜色的数量。

Color video can be represented as vectors. A vector is a mathematical representation of a force in a particular direction. The length of a vector represents the amount of force, and the direction of the vector is where the vector is pointed with respect to a fixed reference, rather like a compass. The piece of equipment used to view and measure these vectors is called a vectorscope (Figure 6.3). Like the waveform monitor, the vectorscope displays an electronic representation of the visual image. (The vectorscope is discussed in more detail in Chapter 8.) In television, the direction of the vector dictates a specific color, and the length represents the amount of that color.

在三芯片彩色摄像机中，三种原色各有一个芯片。每个芯片输出的电压就是矢量的长度。矢量的方向指定为距参考点的度数。在彩色电视中，参考点位于矢量示波器上指向左侧或九点钟方向的水平轴上。该参考点定义为零度。

In a three-chip color video camera, there is one chip for each of the three primary colors. The voltage output from each of these chips is the length of the vector. The direction of the vector is specified as the number of degrees away from a reference point. In color television, the reference point is along the horizontal axis that points to the left, or nine o’clock, on a vectorscope. This reference point is defined as zero degrees.

一切都从那个点开始绕着圆圈，从那里定义了各种颜色。例如，红色定义为从该参考点顺时针旋转 76.5º。蓝色顺时针旋转 192º，绿色略小于 300º（图 6.3）。

Everything goes around the circle from that point, and from there the various colors are defined. For example, red is defined as being 76.5º clockwise from that reference point. Blue is 192º clockwise, and green is just a little less than 300º (Figure 6.3).

彩色连拍

Color Burst

上面提到的参考点是视频信号中称为色同步的部分。彩色突发是彩色副载波的突发或一部分。它未经调制，也不包含任何其他颜色信息。

The reference point mentioned above was the part of the video signal known as color burst. Color burst is a burst or portion of just the color subcarrier. It is not modulated and does not contain any of the other color information.

在后沿或水平消隐期间，突发在模拟波形监视器上显示为一系列周期。它在模拟矢量示波器上显示为从圆心向左或向九点钟方向延伸的线（图 6.3）。它还作为脉冲交叉显示出现在视频监视器上黄绿色条在水平消隐期间沿屏幕下降（见图4.2）。

The burst appears on the analog waveform monitor as a series of cycles during the back porch or the horizontal blanking period. It appears on the analog vectorscope as the line going toward the left, or toward nine o’clock, from the center of the circle (Figure 6.3). It also appears on the video monitor in the pulse cross display as a yellow-green bar going down the screen in the horizontal blanking period (see Figure 4.2).

请注意，由 8 到 11 个子载波周期组成的突发具有幅度和方向，因此实际上具有颜色。该突发被用作接收器的参考，以解码包含在输入视频信号的每一行中的颜色信息。

Note that the burst, which is made up of 8 to 11 cycles of the subcarrier, has an amplitude and direction and thus actually has a color. The burst was used as the reference for a receiver to decode the color information that is contained in each line of the incoming video signal.

色度和亮度

Chrominance and Luminance

颜色可以通过三个测量来定义：（1）色度，颜色信息量；(2) luminance，与颜色信息混合的白光量；(3)色调，特定的彩色颜料。

Color can be defined by three measurements: (1) chrominance, the amount of color information; (2) luminance, the amount of white light that is mixed with the color information; and (3) hue, the particular color pigment.

颜色和光，或色度和亮度的组合产生饱和度。饱和度是信号中有多少颜色和多少光之间的比率（图 6.4，图 5）。如果将更多的白光添加到一种颜色中，它就会变得不饱和。如果去除白光，颜色会变得更饱和。考虑红色和粉红色之间的区别。粉红色与红色的色调相同，只是其中含有更多的白光，从而降低了它的饱和度。在加色系统中添加更多颜色的方法是按比例添加其他两种原色，因为这三种颜色的组合都是白色的。

The combination of color and light, or chrominance and luminance, produces saturation. Saturation is the ratio between how much color and how much light there is in the signal (Figure 6.4, Plate 5). If more white light is added to a color, it becomes desaturated. If the white light is removed, the color becomes more saturated. Consider the difference between red and pink. Pink is the same hue as red, except it has more white light in it, which desaturates it. The method used to add more color in an additive system is to add proportionate amounts of the other two primaries, as the combination of all three is white.

在彩色电视中，向量的长度代表饱和度，向量的方向代表色调。为了能够在电视系统中正确复制颜色，必须准确定义每种颜色的色度与亮度比，以及与参考色同步相关的矢量方向。颜色以度数描述。这

In color television, the length of the vector represents the saturation, and the direction of that vector represents the hue. To be able to replicate colors correctly in a television system, there has to be an exact definition of the chrominance-to-luminance ratio for each color, as well as the direction of the vector in relation to the reference color burst. The colors are described in degrees. The

图 6.4（图 5） 颜色矢量锥

Figure 6.4 (Plate 5) Color Vector Cone

电视中的饱和度或色度与亮度之比以百分比表示。模拟 NTSC 系统中的近似百分比和比率如下：

saturation or chrominance-to-luminance ratio in television is given in percentages. Those approximate percentages and ratios in the analog NTSC system are as follows:

当每个相机芯片或拾取管接收光时，电压输出会根据这些色度和亮度百分比进行分配。例如，如果红色的输出是 1 伏特的视频，那么 3/10 伏特就是亮度，7/10 伏特就是芯片看到的色度。上述比例的三个电视原色的组合将产生白色。

As each camera chip or pickup tube receives light, the voltage output is divided according to these chrominance and luminance percentages. For example, if the output from red is 1 full volt of video, then 3/10 of a volt would be the amount of luminance and 7/10 of a volt would be the amount of chrominance that the chip is seeing. The combination of the three television primaries in the above proportions will give white.

为了将亮度信息与色度信息分开，使用了上述数学计算的另一面。红色定义为 30% 的亮度和 70% 的色度。因此，在红色芯片的输出端检测到的任何电压的 30% 代表了亮度信息。白色是红色芯片输出的30%、绿色59%、蓝色11%的总和。该信号作为黑白信息在主画面载频上传输。在视频中表示亮度的符号是字母 Y。黑白接收器仅使用此信息，而不解码交织在主载波中的颜色信息。

To separate the luminance information from the chrominance, the other side of the mathematical calculation above is used. Red is defined as 30% luminance and 70% chrominance. Therefore, 30% of whatever voltage is detected at the output of the red chip represents the luminance information. White is the sum of 30% of the output of the red chip, 59% of the green, and 11% of the blue. This signal is transmitted as the black and white information on the main picture carrier frequency. The symbol to represent luminance in video is the letter Y. Black and white receivers use only this information and do not decode the color information that is inter-woven in the main carrier.

色差信号

Color Difference Signals

用于创建亮度信号的计算也用于创建色度或色度信息。颜色信息减去亮度信息被称为色差信号。在数学上，这将显示为 Red-Y（红色减去亮度）、Green-Y 和 Blue-Y，或 RY、GY 和 BY。根据毕达哥拉斯定理，只需要两个信号计算颜色信息。选择 RY 和 BY 是因为它们包含最少量的亮度信息，因此可以节省带宽。

The calculations used to create the luminance signal are also used to create the chroma or chrominance information. The color information minus the luminance information is known as the color difference signal. Mathematically, this would be shown as Red-Y (Red minus luminance), Green-Y, and Blue-Y, or R-Y, G-Y, and B-Y. Based on the Pythagorean theorem, only two signals are needed to calculate the color information. R-Y and B-Y were chosen because they contain the least amount of luminance information and therefore conserve bandwidth.

名称 RY 和 BY 后来更改为模拟信号的 Pr 和 Pb，以及数字信号的 Cr 和 Cb。因此，Y、RY、BY 将指定为 Y、Pb、Pr 或 Y、Cb、Cr。随着模拟视频被数字视频取代，Pb 和 Pr 名称不再常用，取而代之的是 Cb 和 Cr 名称。

The designations R-Y and B-Y were later changed to Pr and Pb for analog signals and Cr and Cb for digital signals. Thus, Y, R-Y, B-Y would be designated either as Y, Pb, Pr or as Y, Cb, Cr. As analog video is replaced by digital, the Pb and Pr designations are no longer in common use and are being replaced by the Cb, Cr designations.

传输的色差信号是通过测量红色和蓝色芯片的输出以及亮度信号产生的。这导致矢量彼此相隔 90º，形成直角三角形的两条边——在矢量示波器上，RY 轴向北直行，BY 轴向东直行（图 6.5 ）。

The color difference signals for transmission are created by measuring the output of the red and blue chips and the luminance signal. This results in vectors which appear 90º apart from each other, creating two sides of a right triangle—on a vectorscope, the R-Y axis goes straight north and the B-Y axis goes straight east (Figure 6.5).

一旦测量了来自红色和蓝色输出的颜色信息，简单的算术就可以决定绿色输出是什么，而无需实际获得有关接收信号的信息。这个过程被称为编码和解码颜色。

Once the color information from the red and blue outputs has been measured, simple arithmetic dictates what the green output is without actually having the information on the received signal. This process is known as encoding and decoding color.

在任何给定的时刻，知道矢量长度和角度，接收器中的电路可以重建产生它的 RY 和 BY 信号的原始强度。从这两个信号和 Y，可以计算出 GY 信号。然后通过组合每个色差信号产生彩色电视图像，根据 到定义的百分比，以及视频载体上的亮度信息。

At any given instant, knowing the vector length and angle, circuits in the receiver can reconstruct the original strengths of the R-Y and B-Y signals that produced it. From these two signals and Y, the G-Y signal can be calculated. The color television picture is then produced by combining each of the color difference signals, according to the defined percentages, with the luminance information that was on the video carrier.

图 6.5 矢量显示

Figure 6.5 Vector Display

虽然色差信号最初设计用于提取黑白信号以与单色接收器兼容，但它们仍然存在于数字世界中。人类视觉系统对亮度信息非常敏感，但对色度信息则不太敏感。通过使用色差矩阵数学从相机中产生红色、绿色和蓝色的单独亮度和色度差信号，可以对信号的颜色部分应用不同量的压缩，从而为亮度信息留下更多数据。压缩将在第 14 章中详细讨论。

While the color difference signals were originally designed to allow the extraction of a black and white signal for compatibility with monochrome receivers, they live on in the digital world. The human visual system is very sensitive to luminance information, but less so to chrominance. By using the color difference matrix math to produce separate luma and chroma difference signals of the red, green and blue from the camera, different amounts of compression can be applied to the color part of the signal, leaving more data for the luminance information. Compression will be discussed in detail in Chapter 14.

其他颜色标准

Other Color Standards

与 NTSC 一样，PAL 和 SECAM 也是制作模拟彩色视频信号的方法。PAL 和 SECAM 共享相同的行频和帧速率，这与 NTSC 不同。PAL 和 SECAM 在处理颜色的方式上彼此不同，也与 NTSC 不同。在 PAL 系统中，色差信号在两个独立的副载波上进行编码。这与 NTSC 不同，NTSC 在一个子载波上对两种色差信号进行编码。通过使用两个在时间上彼此相隔 90º 的子载波，颜色相位误差在 NTSC 中表现为色调变化，在 PAL 中表现为彩色图像的轻微饱和度降低。PAL 色彩系统中没有针对饱和度进行调整。信号的那个方面是固定的。由于这种编码过程，PAL 系统中的颜色比 NTSC 中的颜色更真实、更一致。

Like NTSC, PAL and SECAM are ways to make an analog color video signal. PAL and SECAM share the same line frequency and frame rate, which is different than NTSC. PAL and SECAM are different from each other, and from NTSC, in the way they process color. In the PAL system, the color difference signals are encoded on two separate subcarriers. This differs from NTSC, which encodes both color difference signals on one subcarrier. By using two subcarriers 90º apart in time from each other, color phase errors, which appear in NTSC as a change in hue, appear in PAL as a slight desaturation of the color image. There is no adjustment in the PAL color system for saturation. That aspect of the signal is fixed. Because of this encoding process, color in the PAL system is truer and more consistent than it is in NTSC.

在 SECAM 中，色差信号在一个彩色副载波信号上按顺序一次编码一个。接收器存储第一个色差信号，等待第二个色差信号，将两者结合起来，然后创建彩色图像。因为每个色差信号是单独处理的，所以可以编码更大量的信息。由于两种颜色信号都存储在接收器中然后进行解码，因此所获得的颜色是所有三种标准中最好的。

In SECAM, color difference signals are encoded one at a time in sequence on one color subcarrier signal. The receiver stores the first color difference signal, awaits the second, combines both, and creates the color image. Because each of the color difference signals is handled separately, a greater quantity of information can be encoded. As both color signals are stored within the receiver and then decoded, the color achieved is the best of all three standards.

监视器的类型

Types of Monitors

显示器有多种质量等级和广泛的价格范围。在低端，售价几百美元的是作为消费电视显示器出售的电视机。虽然这些可以产生非常好的图像，但它们没有专业显示器所必需的工具。它们的颜色通常设置得令人愉悦而不是准确，以使其更具购买吸引力。

Monitors are available in a number of quality grades and a broad range of prices. At the low end, for a few hundred dollars, are sets sold as consumer television displays. While these can produce a very good image, they do not have the tools necessary that are part of a professional monitor. Their color is often set to be pleasing rather than accurate to make them more appealing for purchase.

中间范围是具有更好色彩再现和控制的专业显示器。它们的成本可能是消费者套装的数倍，主要是因为大规模生产没有效率来帮助支付附加功能的成本。这些监视器适用于大多数一般电视制作应用。它们可能是独立的单一显示器，也可能是多图像处理器，可以在单个大显示器上显示多个小图像。这种类型的显示器经常出现在必须同时查看许多图像的控制室中。

In the middle range are professional monitors that have better color rendition and control. They can cost several times what a consumer set does, primarily as there are no efficiencies in mass production to help defray the cost of the additional features. These monitors are good for most general television production applications. They may be stand-alone single displays, or they may be multi-image processors that can display several small images on a single large monitor. This type of display is often seen in control rooms where many images must be viewable at the same time.

最后，还有用于关键颜色判断的顶级显示器。这些通常出现在精加工编辑套件和色彩校正应用程序中。这些被称为“1 级”或“参考”显示器的设备每台售价数千美元并不罕见。如果您要对高端或广播制作做出最终的色彩判断，这些是需要寻找的单位。

Finally, there are top quality monitors used for critical color judgments. These are often found in finishing editing suites and in color correction applications. Called “Grade 1” or “Reference” monitors, it is not uncommon to see these units costing thousands of dollars each. If you are making the final color judgments on high-end or broadcast productions, these are the units to seek.

视频显示器

Video Displays

显示视频的原始方法是通过使用阴极射线管 (CRT)。这种类型的显示器称为直接视图，接收器或监视器安装在机架上或放置在支架上。屏幕尺寸从几英寸到五十英寸显像管不等。CRT 不再生产，取而代之的是下面描述的几种不同的平面屏幕技术。

The original method of displaying video was through the use of the cathode ray tube (CRT). This type of display is called direct view, with the receiver or monitor being rack-mounted or placed on a stand. The screen size ranges from a few inches up to a fifty-inch picture tube. CRT’s are no longer manufactured, replaced by several different flat screen technologies described below.

投影系统

Projection Systems

投影系统可用作前投和背投类型。在前投影系统中，视频投影仪用于照亮屏幕，其方式与放映电影的方式大致相同。屏幕尺寸可以大到对角线测量一百英寸。背投系统通常有一个内部投影仪和一个将图像反射到屏幕上的镜子，其观看方式与直视式 CRT 大致相同。按对角线测量，观看屏幕的尺寸通常为四十到八十英寸。在旧类型的投影系统中，前后系统都使用三个 CRT——一个红色、一个蓝色和一个绿色——对齐以在屏幕上创建单个图像。

Projection systems are available as front-projection and rear-projection types. In a front-projection system, a video projector is used to illuminate a screen in much the same manner as film is displayed. The screen size can be as large as one hundred inches measured diagonally. Rear-projection systems generally have an internal projector and a mirror to reflect the image on to the viewing screen and are viewed in much the same manner as a direct-view CRT. The viewing screen is generally forty to eighty inches in size, measured diagonally. In the older type of projection systems, both front and rear systems used three CRTs—one red, one blue and one green—that are aligned to create a single image on the viewing screen.

较新类型的显示器包括数字光处理 (DLP)、液晶显示器 (LCD)、硅基液晶 (LCoS) 和等离子。

The newer types of displays include Digital Light processing (DLP), liquid crystal display (LCD), liquid crystal on silicon (LCoS) and plasma.

数码相框

DLP

DLP 使用德州仪器开发的称为数字微镜器件的光学半导体。该设备由数以百万计的微镜组成，这些微镜以矩形阵列排列在硅芯片上，每秒旋转或移动数千次（图 7.1）。它们将光引向或远离特定的像素空间。DLP 投影仪可以使用三个单独的芯片，每个芯片对应一种原色。

The DLP uses an optical semiconductor called a Digital Micromirror Device developed by Texas Instruments. The device is composed of millions of microscopic mirrors arranged in a rectangular array on a silicon chip that rotate or move thousands of times a second (Figure 7.1). They direct light toward or away from specific pixel spaces. DLP projectors can use three individual chips, one for each primary color.

图 7.1 DLP 微镜技术

Figure 7.1 DLP Microscopic Mirrors Technology

还有一种单芯片版本，通过聚光透镜聚焦高强度灯。聚集的光然后通过一个六面板色轮，该色轮将光过滤成红色、绿色和蓝色。每种颜色在滤镜轮上出现两次。光线然后通过整形透镜。这种成形的光源聚焦在芯片上，被微镜反射，然后通过投影镜头投射到屏幕上。镜子的移动和位置在屏幕上创建彩色图像。

There is also a single-chip version that works by focusing a high-intensity lamp through a condensing lens. The condensed light then passes though a six-panel color wheel that filters the light into red, green and blue. Each color appears twice on the filter wheel. The light then passes through a shaping lens. This shaped light source focuses on the chip, is reflected by the microscopic mirrors, and then passes through a projection lens onto a screen. The movement and position of the mirrors creates the color image on the screen.

彩条

Color Bars

传统上用于设置视频监视器的测试信号是彩条。它是国际专业参考，用于确保后续图像的颜色在任何显示器上看起来都与创建时的颜色相同。彩条信号包含设置 CRT 型彩色监视器和信号本身所需的一切，这将在下一章（图 7.2，图 6）中讨论。

The test signal traditionally used to set up a video monitor is color bars. It is the international professional reference used to ensure that the color of the images that follow look the same on any monitor as they did when they were created. The color bar signal contains everything needed to set up a CRT type color monitor and the signal itself, which will be discussed in the following chapter (Figure 7.2, Plate 6).

国际标准化组织 (ISO)（制定国际标准的机构）批准了多种彩条显示器。不同的颜色条具有不同的元素。尽管元素可能不同，但所有彩条信号都具有相同的基本色度和亮度参考。

There are several varieties of color bar displays approved by the International Organization for Standardization (ISO), the agency that sets international standards. Different color bars have different elements. Although the elements may differ, all color bar signals have the same basic chrominance and luminance references.

图 7.2（图 6） 彩条显示

Figure 7.2 (Plate 6) Color Bar Displays

图 7.3 阶梯（灰度）测试图案

Figure 7.3 Stair Step (Gray Scale) Test Pattern

灰阶

Gray Scale

彩条没有参考来设置图片的对比度或明亮部分。为此，称为阶梯或灰度的测试模式非常有用（图 7.3）。该图案可以由测试发生器制作，也可以在视频校准盘上找到。

Color bars do not have a reference to set the contrast or bright part of the picture. For that a test pattern called a stair step or gray scale is very useful (Figure 7.3). This pattern can be made by a test generator or may be found on video calibration disks.

设置监视器

Setting up Monitors

由于模拟 CRT 型显示器在其设置中容易发生漂移，因此鼓励用户每个工作班次至少检查一次显示器设置。虽然目前的显示器能很好地保持其设置，但室内照明的差异可能需要调整显示器以产生最佳画面。虽然在控制室或编辑间不是问题，但当使用监视器的环境中的光量发生显着变化时，应检查用于现场工作的监视器。

Because analog CRT type monitors were subject to drift in their setup, users were encouraged to check the settings of their monitors at least once per work shift. While current displays hold their setting quite well, differences in room lighting may require adjusting monitors to produce the best picture. While not an issue in control rooms or edit bays, monitors used for field work should be checked when there is a significant change in the amount of light in the environment where the monitor is being used.

如果您使用消费品作为显示器，那么在您第一次拿到显示器时进行完整设置非常重要。消费者设备通常设置为在商店等光线明亮的房间内提供最亮的图像。由于您不太可能在如此明亮的空间中工作，因此根据您正在工作的光线水平设置显示器至关重要。

If you are using a consumer product as your monitor, it is important to do a complete setup when you first get the monitor. Consumer equipment is most often set to give the brightest picture possible in a brightly lit room like a store. As you are unlikely to be working in that bright of a space, setting the monitor for the light level you are working in is critical.

许多视频制作者使用计算机显示器作为查看作品的主要方法。计算机并非专为视频工作而设计，可能无法准确显示您的资料。除了显示器的设置外，您还需要调整计算机的视频硬件。找到视频卡的软件控制面板并按照校准说明进行操作，特别注意伽马设置。

Computer monitors are used by many video makers as their main method to view their work. Computers are not designed for just video work, and may not present an accurate display of your material. In addition to the settings for your monitor, you will need to make adjustments to your computer’s video hardware. Find the software control panel for your video card and follow the calibration instructions, paying special attention to the gamma setting.

伽玛曲线

Gamma Curve

伽马是显示器的属性，它处理产生的光量与施加到显示器的电压量之间的关系。较旧的管型显示器是非线性的，这意味着需要不同量的变化电压才能看到图片暗部与亮部的差异。这采用图 7.4中的曲线形式。

Gamma is the property of displays that deals with the relationship of the amount of light produced for the amount of voltage applied to the display. Older tube type displays were non-linear, meaning that it took different amounts of change voltage to see a difference in the dark part of the picture than in the lighter parts. This takes the form of a curve as in Figure 7.4.

图 7.4 伽玛曲线

Figure 7.4 Gamma Curve

早期的广播解决了相机中的这个问题，应用了相反的曲线。通过在相机而不是每台电视机中构建此电路，电视机的价格可能会更便宜。现在使用的显示器类型范围更大，每种显示器类型都具有不同的伽玛特性。然而，我们的视频仍然带有 CRT 的校正因子。因此现在必须调整显示器以适应视频伽马，当您校准计算机的视频卡时通常将其设置为 2.2。

Early broadcasts fixed this problem in the camera, applying an opposite curve. By building this circuit into the camera rather then each TV, sets could be priced more inexpensively. Now a larger range of display types are used, each with different gamma characteristics. Our video, however, still carries the correction factor for CRT’s. So the displays must now be adjusted to suit the video gamma, which is normally set at 2.2 when you are calibrating your computer’s video card.

如何设置监视器

How to Set Up a Monitor

专为视频评估而设计的监视器设计得尽可能中性，以便它们可以用来判断它们所显示的视频信号。然而，消费类设备被配置为产生尽可能“令人愉悦”的画面。如果您选择在专业场合使用这些设备之一，则需要进行一些初始设置。

Monitors designed for video evaluation are designed to be as neutral as possible, so that they can be used to judge the video signal they are displaying. Consumer equipment, however, is configured to produce the most “pleasing” possible picture. Should you choose to use one of these devices in a professional situation, you will need to make some initial settings.

首先，检查并设置色温。任何忘记相机白平衡的人都会告诉您，光线可以从暖黄色到冷蓝色不等。平面电视类型的显示器通常具有将它们设置为暖色或冷色的控件。通常称为“图片模式”或类似的东西，您需要找到调整色温​​的控件并选择最中性的设置。在查看黑白图片时，这是最简单的。如果您的显示器提供标有实际值的色温选项，则正确的选项是 6500K 或 D65。这是日光的近似颜色。

First, check and set the color temperature. As anyone who has forgotten to white balance a camera can tell you, light can vary from a warm yellow to a cool blue. Flat screen TV type monitors often have controls to set them to be warm or cool. Often called “picture mode” or something similar, you need to find the control that adjusts color temperature and choose the most neutral setting. This is easiest when looking at a black and white picture. If your monitor offers color temperature options labeled with actual values, the proper one is 6500K or D65. This is the approximate color of daylight.

接下来找到细节或锐度控制。此功能的目的是使图像看起来更清晰。这是通过在图片中的高频或详细信息周围添加细白边框来实现的。虽然这通常会产生看似更清晰的图像，但它会如果您正在尝试评估镜头的焦点或景深，这将是一个问题。如果没有完全关闭，请将其调低至非常低的设置。

Next find the detail or sharpness control. The purpose of this function is to make images look sharper. This is done by adding a thin white border around high frequency or detailed information in the picture. While this often produces a seemingly crisper image, it will be a problem if you are trying to evaluate a shot for focus or depth of field. Turn this down to a very low setting, if not off completely.

然后关闭动态对比度。消费者显示器的此功能是尝试增加显示器的对比度范围。通过动态改变背光系统的亮度以匹配整体场景亮度，制造商可以声称其显示器具有更好的对比度。但是，如果您使用监视器来判断您的工作质量，此功能可能会掩盖您拍摄中的问题。

Then switch off the dynamic contrast. This function of consumer monitors is to try and increase the contrast range of the monitor. By dynamically changing the brightness of the backlighting system to match overall scene brightness, manufacturers can claim better contrast ratios for their displays. However, if you are using a monitor to judge the quality of your work, this function may mask problems in your shot.

最后，根据您房间的光照水平设置显示器的整体背光强度。如果您在暗室中工作，则不需要显示器的全光输出。设置适当的背光量将使您能够获得适当的亮度和对比度设置并缓解眼睛疲劳。这没有一个确切的值，但您应该设置一个背光级别，使您可以检查材料中的高光并让最黑的部分尽可能暗。

Finally, set the overall backlight intensity of the monitor for light level in your room. If you are working in a dark room, you do not need the full light output of the monitor. Setting the proper amount of backlighting will allow you to get proper setting for brightness and contrast and ease eyestrain. There is not an exact value for this, but you should set a level of backlight that allows you to examine the highlights in your material and lets the blackest parts be as dark as possible.

设置亮度和对比度

Setting the Brightness and Contrast

为不同的房间照明更换显示器的最重要方面是亮度和对比度设置。亮度设置主要影响图像的暗部，而对比度是较亮的部分。最好使用如图 7.3所示的黑白阶梯或灰度图案来完成。

The most important aspects of changing a monitor for different room lighting are the brightness and contrast settings. The brightness setting primarily affects the dark part of the images, while contrast is the brighter parts. This is best done with a black and white stair step or gray scale pattern as shown in Figure 7.3.

从对比度控制开始，调整显示器，使阶梯图案上最亮的两个芯片刚好不同。通常最简单的方法是向上转动控制杆，然后慢慢降低它，观察是否出现差异。接下来使用亮度控制设置两个最暗的芯片，使它们恰到好处不同的。设置亮度后返回并再次检查与白色芯片的对比度。控件相互作用，可能需要来回调整一些才能使设置恰到好处。

Start with the contrast control and adjust the monitor so that the brightest two chips on the stair step pattern are just different. It is often easiest to do this by turning the control way up and then slowly lowering it, watching for a difference to appear. Next use the brightness control to set the two darkest chips so they are just different. After you set brightness go back and check the contrast with the white chips again. The controls interact and it could take a few back and forth adjustments to get the setting just right.

设置颜色

Setting the Color

下一步是设置颜色的数量和颜色的色调（或色调）。为此，您需要使用 SMPTE 条，并且能够只查看蓝色通道输出。专业显示器具有仅蓝色设置，可关闭显示器的红色和绿色通道。消费设备和计算机显示器通常没有该设置。要在消费者显示器上设置颜色和色调，您需要在眼睛上方使用蓝色滤镜，以完全阻挡红光和绿光。您可以尝试多种厚度的蓝色照明凝胶或摄影滤镜，直到找到有效的组合。

The next step is to set the amount of color and the hue (or tint) of the color. To do this you need to use SMPTE bars and be able to look at just the blue channel output. Professional monitors have a blue-only setting that turns off the red and green channels to the monitor. Consumer equipment and computer monitors most often do not have that setting. To set the color and hue on a consumer monitor, you will need to use a blue filter held over your eye that completely blocks the red and green light. You can experiment with several thicknesses of blue lighting gel or photographic filters until you find a combination that works.

在 SMPTE 彩条图案中，有四个彩条下方的小色块。这些筹码的排列方式使其包含与其上方的条相同数量的蓝色内容。调整颜色控制，使外部条和芯片（白色和蓝色）具有相同的阴影。然后调整色调控制，使内部条（品红色和青色）匹配。同样，您可能会发现这些设置之间存在少量交互。

In a SMPTE color bar pattern, there are small chips of color located below four of the color bars. These chips are arranged so they contain the same amount of blue content as the bars above them. Adjust the color control so that the outer bars and chips (the white and blue) are the same shade. Then adjust the hue control so that the inner bars (magenta and cyan) match. Again, you may find a small amount of interaction between these settings.

彩色图像工具

Color Image Tools

上述程序将很好地获得像样的显示。但是，为了获得更好的结果，可以使用旨在帮助设置监视器的工具。

The above procedures will do a good job of getting a decent display. However, for an even better result, there are tools designed to help set up monitors.

第一个是视频校准蓝光光盘。这些磁盘具有旨在帮助设置家庭影院的测试模式和说明系统。他们还将帮助实现非专业的监视器设置。作为奖励，有些带有蓝色滤镜，您需要在没有仅限蓝色功能的显示器上设置颜色和色调。

The first is a video calibration Blu-Ray disk. These disks have test patterns and instructions designed to help set up home theater systems. They will also help achieve a non-professional monitor setup. As a bonus, some come with the blue filter you need to set color and hue on monitors without the blue-only function.

然而，为了获得最准确的设置，应使用称为色度计的设备来正确平衡显示器的 RGB 值。色度计是一种靠在显示器表面的测光表。这些设备可让您测量和平衡显示器产生的红光、绿光和蓝光的数量。

For the most accurate setup, however, a device called a Colorimeter should be used to properly balance the RGB values of the display. Colorimeters are a form of light meter that is held against the surface of the display. These devices let you measure and balance the amount of red, green and blue light produced by the display.

包起来

Wrap Up

选择哪种显示器需要一些妥协。显而易见的答案是为每个应用程序选择预算允许的最佳质量图片。关键评估单元的预期质量水平与仅需要验证信号存在的监视器的质量水平完全不同。

Which display to choose requires a bit of compromise. The obvious answer is to select the best quality picture that a budget allows for each application. The level of quality expected for a critical evaluation unit is entirely different than that for a monitor that is only necessary to verify the presence of a signal.

彩条

Color Bars

在上一章中，您了解到彩条用于设置视频监视器。相同的颜色条用于测量视频信号路径的质量。作为最常见的测试信号，彩条有几种不同的表现形式，包括全场条、EIA 分场条和 SMPTE。这些是随着时间的推移而开发的，以解决视频设置过程的不同方面。

In the previous chapter, you learned that color bars were used to set up a video monitor. The same color bars are used to measure the quality of a video signal path. As the most frequently seen test signal, color bars come in several different presentations, including full field bars, EIA split field bars, and SMPTE. These were developed over time to address different aspects of the video setup process.

SMPTE 条形信号包含一个 100% 的白色芯片、一个 75% 的白色芯片以及三种原色和三种二次色。有一个黑色芯片，在数字世界中测量为 0%，在模拟域中测量为 7.5%。黑色芯片中包含两个较小的芯片。一种是比黑色“暗”几个单位，一种是“亮”几个单位。这些芯片组成了 PLUGE（图片阵容生成设备）。该信号旨在帮助设置显示器的亮度。调整亮度，使较亮的芯片刚好可见，而较暗的芯片与其周围区域融合，将确保正确的黑电平设置（图 8.2，图 7）。

The SMPTE bar signal contains a 100% white chip, a 75% white chip, and the three primary and three secondary colors. There is a chip for black, which measures 0% in the digital world or 7.5% in the analog domain. Contained in the black chip are two smaller chips. One is a few units “darker” than black and one is a few units “brighter.” These chips make up the PLUGE (Picture Lineup Generating Equipment). This signal is designed to help set the brightness on monitors. Adjusting the brightness so the brighter chip is just visible and the darker merges with the area around it will insure a proper black level setting (Figure 8.2, Plate 7).

真实视频通常达不到彩条图案中包含的电平，因为彩条按其意图设计用于指示信号的限制（即最高亮度电平、最高色度电平、最低亮度和很快）。如果颜色以其真实值的 100% 显示在彩条显示中，则参考信号将超出模拟波形监视器的测量能力。例如，SMPTE 将黄色定义为完全饱和时的 133 IRE 单位。模拟波形上的格线不超过 120 IRE 单位。为此，彩条信号减少 到 75% 的真实水平被创建，并且这个 75% 的颜色条是使用的一般标准。75% 颜色条显示中的黄色条显示为 100 IRE 单位。

True video generally does not reach the levels that are contained in a color bar pattern, because color bars by their intent are designed to indicate the limits of the signal (i.e., the highest luminance level, the highest chrominance level, the lowest luminance, and so on). If the colors were presented in the color bar display at 100% of their true values, the reference signals would be beyond the measuring capabilities of the analog waveform monitor. For example, SMPTE defines yellow as 133 IRE units when fully saturated. The graticule on the analog waveform does not measure beyond 120 IRE units. For this reason, a color bar signal reduced to 75% of true levels was created, and this 75% color bar is the general standard in use. The yellow bar in the 75% color bar display appears as 100 IRE units.

图 8.2（图 7） PLUGE 条信号

Figure 8.2 (Plate 7) PLUGE Bars Signal

模拟波形监视器

Analog Waveform Monitors

波形监视器用于确保视频信号的录制或再现符合广播规格。在波形监视器上分析视频信号时，可以更改信号视图并放大某些部分以进行测量。拍摄时视频信号不受影响这些测量值。如果需要调整视频信号以满足广播要求，则需要对视频源本身进行这些更改。这可能是相机、录像机或回放机，或者可能来自编辑应用程序。

The waveform monitor is used to make sure the video signal is being recorded or reproduced within broadcast specifications. When analyzing the video signal on a waveform monitor, the view of the signal can be changed and certain parts enlarged in order to take measurements. The video signal is not affected as you take these measurements. If the video signal needs to be adjusted to meet broadcast requirements, those changes are made on the video source itself. That might be the camera, a video recorder or playback machine, or possibly from within an editing application.

波形监视器显示信号的两个方面，时间和电压。从左到右（沿 X 轴），显示时间。信号早期发生的事情将显示在左侧，而右侧显示时间较晚发生的事情。从上到下（沿 Y 轴）用于测量存在的信号量或信号电压。将两者结合起来，操作员可以及时查看在任何时间点存在的信号量。

The waveform monitor shows two aspects of a signal, time and voltage. From left to right (along the X axis), time is displayed. Things that happen early in a signal will be displayed on the left, while the right side displays what happens later in time. Top to bottom (along the Y axis) is used to measure the amount of signal present, or the voltage of the signal. Combining the two allows the operator to see how much signal is present at any point in time.

标线

Graticule

模拟波形监视器有一个小型 CRT（阴极射线管），可以显示视频图像的电子表示。CRT 前面是一块玻璃或塑料板，称为 CRT标线。CRT 标线由用于测量视频信号的垂直线和水平线组成。水平线采用 IRE视频单位，这是无线电工程师协会 (IRE) 最先开发的测量值。IRE 范围从 –40 到 100 个单位。从 –40 到 100 IRE 的测量值称为一伏视频峰峰值（图 8.3）。

Analog waveform monitors have a small CRT (cathode ray tube) that displays an electronic representation of the video image. In front of the CRT is a glass or plastic plate known as the CRT graticule. The CRT graticule is made up of vertical and horizontal lines used to measure the video signal. The horizontal lines are in IRE units of video, measurements that were first developed by the Institute of Radio Engineers (IRE). The IRE scale ranges from –40 to 100 units. The measurement from –40 to 100 IRE is referred to as one volt of video peak-to-peak (Figure 8.3).

零单位处的水平线称为基线（图 8.3）。它以微秒为单位标有垂直刻度 和十分之一微秒。最短的垂直线代表 2/10 微秒，每五分之一 2/10 微秒是一条稍高的线，代表 1 微秒刻度，或 1。

The horizontal line at zero units is referred to as the base line (Figure 8.3). It is marked with vertical divisions in microseconds and tenths of microseconds. The shortest vertical lines represent 2/10 of a microsecond, and at every fifth 2/10 of a microsecond is a slightly taller line that represents a 1-microsecond division, or 1.

图 8.3 波形格线

Figure 8.3 Waveform Graticule

格线上的信号分量

Signal Components on Graticule

在波形上读取模拟复合信号时，视频信号的零单位线始终设置在格线的基线上。水平同步脉冲应位于基线下方的 –40 单位线上。信号的色同步信号部分应从 –20 IRE 单位到 +20 IRE 单位，总共 40 IRE 单位（图 8.4，图 8）。

When reading an analog composite signal on the waveform, the zero-units line of the video signal is always set on the base line of the graticule. The horizontal sync pulse should be at the –40 units line beneath the base line. The color burst portion of the signal should reach from –20 IRE units to +20 IRE units, for a total of 40 IRE units (Figure 8.4, Plate 8).

图 8.4（图 8） 波形监视器上的彩条

Figure 8.4 (Plate 8) Color Bars on Waveform Monitor

仅从亮度来看，活动视频信号在监视器上占据 7.5 到 100 单位的范围。在图 8.2中，视频彩条的白色部分生成波形显示的顶部。格线顶部附近的水平线应与彩条信号的纯白色方块相匹配，等于 100 个单位。模拟黑色，也称为设置或基座, 是信号最暗的部分，应该位于 7.5 单位虚线上，10 单位线下方 2.5 单位。适当的 100% 视频信号将在格线刻度上测量从水平同步到白峰的 140 个单位。同样，水平同步占据 –40 到 0 个单位之间的部分，而活动视频图像从 7.5 扩展到 100 个单位。

The active video signal, when viewed as luminance only, occupies the range between 7.5 units and 100 units on the monitor. In Figure 8.2, the white portion of the video color bars generates the top part of the waveform display. The horizontal line near the top of the graticule, which should match the pure white square patch of the color bar signal, is equal to 100 units. Analog black, which is also referred to as setup or pedestal, is the darkest part of the signal and should be on the 7.5 units dotted line, 2.5 units below the 10 unit line. A proper 100% video signal will measure 140 units on the graticule scale from the horizontal sync to the white peaks. Again, horizontal sync takes up the portion between –40 and 0 units, while the active video image extends from 7.5 to 100 units on the scale.

信号测量

Signal Measurement

波形监视器能够更改示波器从左到右显示的时间。通常，如图8.4所示，这种调整称为 SWEEP。虽然默认显示 2 个完整行，但可以更改时间以同时显示两个字段中的所有行。以类似的方式，可以在垂直或水平轴上扩展或放大信号以进行更仔细的检查。

Waveform monitors have the ability to change how much time is displayed from the left to the right of the scope. Often, such as in Figure 8.4, this adjustment is called SWEEP. While the default is to show 2 full lines, the time can be changed to show all the lines in both fields simultaneously. In a similar fashion the signal can be expanded, or magnified in either the vertical or horizontal axes for closer examination.

过滤器

Filters

通过向模拟视频信号添加彩色副载波，示波器需要能够分离两个信号以分别进行检查。在图 8.4的输入部分，标记为 FILTER 的按钮选择显示的亮度和色度内容。平面显示器显示信号组合的亮度和色度。低通 (LPASS) 仅选择信号的亮度部分。同样，色度 (CHRM) 单独选择信号的颜色部分。图 8.5显示了一半的范围，左侧滤掉了彩色副载波，并在右侧与亮度相结合。

With the addition of the color subcarrier to the analog video signal, scopes needed the ability to separate the two signals for inspection separately. In the Input section of Figure 8.4, the button marked FILTER selects the content of the display as far as luminance and chrominance are concerned. A FLAT display shows the luminance and chrominance of the signal combined. Low Pass (LPASS) selects the luminance portion of the signal only. Likewise, chrominance (CHRM) selects the color portion of the signal alone. Figure 8.5 shows half the scope with the color subcarrier filtered off on the left, and combined with the luminance on the right.

图 8.5 低通显示

Figure 8.5 Low Pass Display

参考

Reference

波形监视器需要知道何时以与视频监视器相同的方式开始扫描过程。参考同步就是这样做的。参考按钮 (REF) 用于选择内部或外部参考。在内部模式下，显示屏上显示的同步信号还会触发示波器上行和帧的开始。外部参考 (EXT) 用于将示波器与单独的同步源同步。然后可以根据该参考及时测量来自照相机或录音机等设备的信号。这个同步过程被称为视频定时。为了在信号之间干净地切换，每个设备的同步脉冲必须完全对齐，而视频定时是根据外部参考测量调整到达示波器的每个信号的过程。

Waveform monitors needed to know when to start the scanning process in the same way a video monitor did. Reference Sync does just that. The reference button (REF) is used to select either an internal or external reference. In the Internal mode the sync signal that is shown on the display also triggers the start of lines and frames on the scope. External reference (EXT) is used to synchronize the scope with a separate source of sync. Then the signals from devices such as cameras or recorders can be measured in time against that reference. This synchronization process is referred to as video timing. In order to switch cleanly between signals, each device’s sync pulses must perfectly align, and video timing is the process of adjusting each signals arrival at the scope as measured against the external reference.

查看图像

Viewing an Image

彩条信号包含以有序方式出现的精确量和持续时间的色度和亮度。该信号用于确保随后的视频图像符合特定标准的规范。然而，当在波形监视器上查看视频图像时，示波器反映了视频图像的色度和亮度水平，这些水平永远不会像彩条信号那样精确和有序。通常，在整个信号范围的波峰和波谷上分布着各种各样的图像元素（图 8.6）。

A color bar signal contains precise amounts and durations of chrominance and luminance that appear in an ordered fashion. This signal is used to ensure the video images that follow will fall within the specifications of a specific standard. However, when video images are viewed on a waveform monitor, the scope reflects the chrominance and luminance levels of the video image, which never appear as precise and ordered as color bar signals. Often, there is a wide variety of image elements spread over the peaks and valleys of the entire signal range (Figure 8.6).

图 8.6 波形图像

Figure 8.6 Image on Waveform

模拟矢量示波器

Analog Vectorscopes

矢量示波器是另一种用于测量视频信号的示波器。与测量视频信号的亮度和时序方面的波形监视器不同，矢量示波器用于测量饱和度和色调。名称向量来自数学。矢量是具有大小和方向的几何形式。对于视频仪器，方向是在一个圆圈中测量的，很像钟面，代表颜色的色调。颜色的大小或数量是饱和度，它是用到圆心的距离来衡量的。

The vectorscope is another type of oscilloscope used to measure the video signal. Unlike the waveform monitor, which measures the luminance and timing aspects of a video signal, a vectorscope is used to measure the saturation and hue. The name vector comes from mathematics. A vector is a geometric form that has magnitude and direction. For video instruments the direction is measured in a circle, much like a clock face, and represents the hue of the color. The magnitude or amount of the color is the saturation, which is measured as the distance from the center of the circle.

标线

Graticule

与波形监视器一样，矢量示波器有一个显示信号的小型 CRT。CRT 在一块玻璃或塑料板后面，上面刻有一个带有标记和线条的圆圈，这就是标线（图 8.7）。圆圈本身的标记代表从 0 到 360 度的度数。较细的、单独的凹口或标记代表 2 度的差异。较粗的标记代表 10 度。0 点或标记位于示波器上九点钟的位置。度数标记从该点开始沿顺时针方向移动。

As with waveform monitors, vectorscopes have a small CRT that displays the signal. The CRT is behind a glass or plastic plate inscribed with a circle that had markings and lines, which is the graticule (Figure 8.7). The markings on the circle itself represent degrees from 0 to 360. The thinner, individual notches or markings represent differences of 2 degrees. The bolder markings represent 10 degrees. The 0 point or mark is at a nine o’clock position on the scope. The degree markings move in a clockwise position from that point.

轴

Axes

有两条垂直线水平和垂直穿过圆。从 0º 到 180º 的线称为X 轴。从 90º 到 270º 的垂直上下线称为Y 轴。模拟示波器有第二组轴，用于测量复合信号中的副载波。这组称为 I 和 Q，不用于数字信号。

There are two perpendicular lines that cut horizontally and vertically through the circle. The line that goes from 0º to 180º is referred to as the X axis. The vertical up and down line that goes from 90º to 270º is called the Y axis. Analog scopes have a second set of axes, used to measure the subcarrier in a composite signal. This set, called I and Q, are not used with digital signals.

图 8.7 矢量示波器刻度线

Figure 8.7 Vectorscope Graticule

矢量读数

Vector Readings

在格线上，圆圈内有单独的方框。从九点钟位置开始顺时针方向移动，分别是黄色 (YL)、红色 (R)、品红色 (MG)、蓝色 (B)、青色 (CY) 和绿色 (G)。红色、蓝色和绿色这三种原色中的每一种都被一种二次色隔开。二次色是它两侧的两种原色的混合。方框放置表示特定矢量的方向或色调。这些框还用作矢量的正确长度或其饱和度的指示。

On the graticule, there are individual boxes that are located within the circle. Starting from the nine o’clock position and moving clockwise, these are yellow (YL), red (R), magenta (MG), blue (B), cyan (CY), and green (G). The three primary colors, red, blue, and green, are each separated by one of the secondary colors. The secondary color is a mixture of the two primary colors on either side of it. The box placement represents the direction or hue of a particular vector. The boxes are also used as an indication of the correct length of a vector, or its saturation.

正确设置彩条的色度信号会显示信号的中心点与圆刻度的中心点对齐（图 8.8）。彩色副载波信号的突发，X 轴上的短线，应直接指向

The proper setup of the chrominance signal for color bars would show the center point of the signal aligned with the center point of the circle scale (Figure 8.8). The burst of the color subcarrier signal, the short line on the X axis, should point directly to the

图 8.8 矢量示波器

Figure 8.8 Vectorscope

九点钟的位置。就像波形上的视频图像一样，颜色条被设计为适合矢量示波器中的特定颜色框。

nine o’clock position. Much like a video image on the waveform, the color bars were designed to fit into specific color boxes in the vectorscope.

活动视频

Active Video

在活动视频期间，矢量示波器不显示直线和尖点。显示屏显示出一团模糊的能量。这个斑点代表电视画面中的各种颜色，而不是彩条信号中存在的纯色。

During active video, the vectorscope does not show straight lines and sharp dots. The display shows a fuzzy blob of energy. This blob represents the variety of colors in the television picture rather than the pure colors that existed in a color bar signal.

包起来

Wrap Up

自模拟视频以来，技术发生了很大变化，但重要的是要记住，它是我们今天处理和测量视频的方式的基础。下一章讨论用于测量数字视频信号的软件和测试设备。

Technology has changed a lot since analog video, but it’s important to keep in mind that it was the basis of how we work with and measure video today. The following chapter discusses the software and test equipment used to measure the digital video signal.

数字信号

The Digital Signal

虽然数字信号与模拟信号一样，峰峰值为 1 伏，但在数字示波器上显示和测量该 1 伏内的某些组件和测量值有所不同。一伏特分为千个单位，每个单位称为毫伏，用mV表示（图9.2）。在标线上，1 伏数字视频显示为从 –.3 伏（或 –300 毫伏）到 0.7 伏（或 700 毫伏）的峰值，总计 1 伏。活动数字视频显示在标线的 0 基线和 0.7 伏之间。这与模拟波形监视器上的 100% 视频或 100 IRE 单位有关。

While the digital signal, as with analog, is 1 volt peak-to-peak, some of the components and measurements within that 1 volt are displayed and measured differently on a digital scope. One volt is divided into a thousand units, each referred to as a millivolt, expressed as mV (Figure 9.2). On the graticule, 1 volt of digital video is displayed from –.3 volts (or –300 mV) to a peak of .7 volts (or 700 mV) for a total of 1 volt. Active digital video is displayed between the 0 base line on the graticule and .7 volts. This relates to 100% video, or 100 IRE units on an analog waveform monitor.

由于数字信号是数字信息流，因此它不需要与模拟信号相同的同步元素。同步现在由每行视频上的两个短数据突发处理，称为定时参考信号或 TRS。该信号由 40 位或 4 个 10 位字组成，其中包含标识活动视频开始 (SAV) 和活动视频结束 (EAV) 的标志。

Since the digital signal is a stream of digital information, it does not require the same synchronization elements that an analog signal did. Sync is now handled by two short data bursts on each line of video called Timing Reference Signal or TRS. This signal consists of 40 bits, or 4 10-bit words, that contain flags that identify the Start of Active Video (SAV) and End of Active Video (EAV).

当信号显示在数字波形监视器上时，信号中没有水平或垂直同步显示（图 9.3）。在矢量示波器上，没有同步色同步，它通常出现在矢量示波器刻度线的九点钟位置。

When a signal is displayed on a digital waveform monitor, there is no horizontal or vertical sync display within the signal (Figure 9.3). On a vectorscope, there is no synchronizing color burst, which used to appear in the nine o’clock position on the vectorscope graticule.

虽然模拟黑色以 7.5 IRE 单位显示，但数字信号中的真黑色为 0 伏，因此显示在标线的基线处。由于模拟传输系统被设计为在较低的视频电平下输出峰值功率，如果模拟黑信号是真黑或 0 单位，则模拟信号可能会使发射器电气过载。由于数字信号是数据流或数字位，因此电平不会随时间变化，而是保持不变。因此，数字视频可以利用纯黑和全亮度之间的整个范围。

While analog black was displayed at 7.5 IRE units, true black in a digital signal is 0 volts, and is therefore displayed at the baseline on the graticule. Because the analog transmission system was designed to put out peak power at the lower video levels, if the analog black signal were true black, or 0 units, the analog signal could electrically overload the transmitter. Since a digital signal is a stream of data or digital bits, the levels do not vary over time, but instead remain constant. As a result, digital video can utilize the full range between true black and full luminance.

图 9.2 数字波形监视器

Figure 9.2 Digital Waveform Monitor

图 9.3 没有同步的数字信号

Figure 9.3 Digital Signal without Sync

与以 IRE 单位标记的旧式模拟波形监视器不同，数字示波器刻度上的刻度以毫伏 (mV) 为单位，范围从 –300 mV 到 +800 mV，每个主要格进一步细分为五个小格，每个代表 20 毫伏（图 9.3）。水平参考线或基线是 0 处的粗线，在 –.1 和 .1 线之间有三个大的垂直标记。这条线交替称为 0% 线、0 mV、零线、消隐电平和黑电平。

Unlike the older analog waveform monitors marked in IRE units, the scale on the graticule of a digital scope is marked in millivolts (mV) and ranges from –300 mV to +800 mV, with each major division being further subdivided into five minor divisions, each one representing 20 millivolts (Figure 9.3). The horizontal reference line, or base line, is the heavy line at 0 with three large vertical markings between the –.1 and .1 lines. This line is alternately referred to as the 0% line, 0 mV, zero line, blanking level, and black level.

软件数字示波器显示

Software Digital Scope Displays

除了经典模拟示波器的波形和矢量显示外，现代示波器还可以显示其他信号属性。有些是大多数示波器型号所共有的，而另一些则是特定制造商或型号独有的专有显示器。许多视频内容创建者都可以访问内置在他们计算机上的软件应用程序中的示波器显示。

In addition to the waveform and vector displays from classic analog scopes, there are other signal attributes that can be displayed by modern scopes. Some are common to most models of scopes, and others are proprietary displays unique to a specific manufacture or model. Many video content creators have access to scope displays that are built into a software application on their computers.

测量亮度

Measuring Luminance

在图 9.4（图 9）中，图像（在本例中为彩条）显示在右侧，图像（彩条）的亮度波形显示在左侧，如在 Apple 的 Final Cut Pro 编辑应用程序中所见. 该显示是模拟波形监视器显示亮度级别的方式的数字再现。基于软件的示波器的一个优点是它们通常会显示它们在显示器中代表的颜色，使操作员更容易找到代表视频图像内容的显示器部分。如果您查看色板9中的此图像，您可以看到每个颜色条都由波形显示中该条的颜色表示。

In Figure 9.4 (Plate 9), the image, in this case color bars, is displayed on the right side, and the luminance waveform display of the image (color bars) is on the left, as seen in Apple’s Final Cut Pro editing application. This display is a digital recreation of the way analog waveform monitors show luminance levels. One advantage of software-based scopes is that they often show the color they are representing in the display, making it easier for the operator to find the part of the display that represents what is in the video image. If you look at this image in color Plate 9, you can see that each color bar is represented by that bar’s color in the waveform display.

在图 9.5（图 10）中，正常的视频场景显示在监视器的右侧，亮度波形显示为

In Figure 9.5 (Plate 10), a normal video scene is represented on the right side of the monitor and the luminance waveform display of

图 9.4（图 9） 软件范围上的颜色条

Figure 9.4 (Plate 9) Color Bars on Software Scope

图 9.5（图 10） 软件示波器上的正常视频场景

Figure 9.5 (Plate 10) Normal Video Scene on Software Scope

该图像在左侧。在波形显示中，请注意较高的亮度级别（几乎显示为水平波浪线），它代表明亮的天空。仔细观察那个区域，您可以看到白云从哪里开始和停止。请注意显示屏中间明显的垂直 V 形下沉。当你看右边的图像时，你会看到雕像的黑暗造成了倾角，这比云暗得多。

that image is on the left. In the waveform display, notice the upper luminance levels (appearing almost as horizontal wavy lines), which represent the bright sky. Look closely at that area and you can see where the white clouds start and stop. Notice the sharp vertical V-like dip in the middle of the display. When you look at the image on the right, you see that dip is created from the darkness of the statue, which is much darker than the clouds.

具有静态摄影背景的内容创建者可能会识别直方图显示（图 9.6）。直方图显示是图像编辑程序（如 Adob​​e 的 Photoshop）中使用的主要测量工具。直方图将数字图像中暗区和亮区的分布显示为像素密度显示。直方图显示在水平轴和垂直轴内。水平轴表示从标尺左端的黑色到标尺右端的白色的亮度级别。像素密度在垂直轴上读取，密度从垂直轴底部的低密度增加到垂直轴向上移动的更高密度。例如，显示器右侧的山状密集像素块图 9.6代表图像中最亮的部分，在本例中是白云和明亮的天空。

Content creators with a still photography background may recognize the Histogram display (Figure 9.6). The Histogram display is the predominant measuring tool used in image editing programs such as Adobe’s Photoshop. A Histogram shows the distribution of dark and light areas within the digital image as a pixel density display. The Histogram is displayed within horizontal and vertical axes. The horizontal axis represents levels of brightness from black at the left end of the scale to white at the right end of the scale. Pixel density is read on the vertical axis with the density increases shown from low density at the bottom of the vertical axis, to higher density moving up the vertical axis. For example, the mountain-like clump of dense pixels on the right side of the display in Figure 9.6 would represent the brightest part of the image, in this case the white clouds and bright sky.

在沿水平轴的每个亮度级别，显示线的高度表示该特定亮度级别的像素密度。该亮度级别的像素越多，显示线就越高。因此，图像的暗区集中在左侧的直方图显示上，图像的亮区沿水平轴显示在更远的右侧。明亮的图像会使直方图偏向显示的右端，而主要是暗的图像会偏向左侧。均匀照明的图像会使像素密度显示分布得更多

At each level of brightness along the horizontal axis, the height of the display line indicates the pixel density at that specific light level. The more pixels at that level of brightness, the taller the display line. Thus, dark areas of the image are concentrated on the Histogram display at the left side and bright areas of the image are shown farther to the right along the horizontal axis. Bright images would skew the Histogram toward the right end of the display and predominantly dark images would skew more toward the left. An evenly lit image would distribute the pixel density display more

图 9.6 直方图显示

Figure 9.6 Histogram Display

均匀分布在直方图屏幕上。在运动图像中，直方图将随着图像的变化而不断变化。

evenly across the Histogram screen. In motion images, the Histogram will be constantly changing as the images change.

许多图像处理程序使用直方图显示作为其用户界面的一部分来调整级别。在图 9.7中，Adobe After Effects 中的色阶滤镜显示了直方图，黑色色阶设置为典型色阶，然后黑色被压碎。请注意左侧直方图显示左端下方的小三角形（圆圈）。这用作图像暗部的控件，并指示要裁剪多少暗像素以生成第二张图像。右边的图像显示了更靠右的小三角形，从而产生了整体较暗的图像。

Many image-processing programs use the Histogram display as part of their user interface for adjusting levels. In Figure 9.7, the Levels filter in Adobe After Effects shows the Histogram with the black levels set to a typical level, then with the blacks crushed. Note the small triangle below the left end of the Histogram display on the left (circled). This acts as the control for the dark parts of the image and indicates how many dark pixels are being clipped to produce the second image. The image on the right shows the small triangle further to the right, producing an overall darker image.

图 9.7 显示默认图像（左）和图像变暗（右）的级别过滤器

Figure 9.7 Levels Filter Showing a Default Image (left) and with the Image Made Darker (right)

测量颜色信息

Measuring Color Information

要测量颜色，您通常会使用矢量示波器。与其模拟前辈一样，颜色的色调是围绕圆圈的位置，而饱和度是从显示器中心向外的距离。在图 9.8（图 11）中，您可以看到颜色条矢量显示的数字表示。与图 9.4中的颜色条图像一样，此显示中的矢量采用它们所代表的颜色。

To measure color, you often use a Vectorscope. Like its analog predecessors, the hue of the color is the position around the circle, while the saturation is the distance outward from the center of the display. In Figure 9.8 (Plate 11), you see a digital representation of a vector display of color bars. Like the color bars image in Figure 9.4, the vectors in this display take on the color they are representing.

图 9.8（图 11） 在软件矢量示波器上显示的颜色条

Figure 9.8 (Plate 11) Color Bars Displayed on Software Vectorscope

图 9.9（图 12） 在软件矢量示波器上显示的视频场景

Figure 9.9 (Plate 12) Video Scene Displayed on Software Vectorscope

这里一个非常有用的标记是从示波器中心延伸到左上角的线，位于黄色和红色矢量之间。这是肤色线，在处理某些面部特写镜头时会很有帮助。在图 9.9（图 12）中，黄金 雕像和黄色花朵导致矢量显示向肤色线倾斜。

One very useful marker here is the line from the center of the scope that extends to the upper left, between the yellow and red vectors. This is the skin tone line, which can be helpful when working with certain close up shots of faces. In Figure 9.9 (Plate 12), the gold statue and yellow flowers are causing the vector display to lean toward the skin tone line.

视频中的颜色量或饱和度也显示在 Vectorscope 显示器中。在图 9.10a（图 13）中，Avid Media Composer 颜色校正工具中的矢量显示显示具有正常饱和度的图像。在第二个版本中，图 9.10b（图 14），同一图像的饱和度增加到 200%。请注意图像中间出租车上的红色条纹。在饱和版本中，矢量示波器中的红色能量几乎延伸到彩条中红色条的方框。

The amount of color, or saturation, in video is also displayed in a Vectorscope display. In Figure 9.10a (Plate 13), the vector display in the Avid Media Composer color correction tool shows an image with normal saturation. In the second version, Figure 9.10b (Plate 14), the saturation for the same image is increased to 200 percent. Notice the red stripe on the taxi in the middle of the image. On the saturated version, the red energy in the Vectorscope reaches out nearly to the box for the red bar in color bars.

图 9.10a（图 13） 正常饱和度

Figure 9.10a (Plate 13) Normal Saturation

图 9.10b（图 14） 增加的饱和度

Figure 9.10b (Plate 14) Increased Saturation

还有其他方法可以在示波器中查看图像的颜色部分。例如，图 9.11a（图 15）是所谓的游行模式下的波形显示。在游行模式中，各个颜色通道一个接一个地显示，分别表示红色、绿色和蓝色。此显示对于设置镜头中的色彩平衡很有用。在视频场景中（图 9.11b，图 16），您可以看到蓝色级别高于红色或绿色，这意味着图像中有更多的蓝色。

There are other ways to view the color portion of an image in scopes. For example, Figure 9.11a (Plate 15) is a waveform display in what is referred to as Parade Mode. In Parade Mode, the individual color channels are shown one after the other with separate representations for red, green and blue. This display is useful to set color balance in a shot. In the video scene (Figure 9.11b, Plate 16), you can see the blue levels are higher than red or green, meaning there is a bit more blue in the image.

图 9.11a（图 15） 游行模式下的彩条

Figure 9.11a (Plate 15) Color Bars in Parade Mode

图 9.11b（图 16） 阅兵模式视频场景

Figure 9.11b (Plate 16) Video Scene in Parade Mode

色域

Color Gamut

在视频信号和其他颜色再现领域（如视频监视器和计算机图形）中，存在构成特定颜色空间或色域的允许值范围或色域。视频中的色彩空间被定义为具有三个属性。例如，一种颜色空间 RGB 使用三种原色，即红色、绿色和蓝色。另一种颜色空间使用亮度和色差信号，或 Y、Cr、Cb。HSV 空间通过其色调、饱和度和值（或亮度）定义颜色。这些颜色空间中的每一个都包含在其他颜色空间之一中可能无法再现的颜色。提到 4K/UHD 视频，很多人首先想到的可能是其更高的图像分辨率。但它也可以产生比 HDTV 视频更广泛的颜色范围或色域（图 9.12（图 17））。

In a video signal, and other areas of color reproduction such as video monitors and computer graphics, there is a range or gamut of allowable values that make up a specific color space or color gamut. Color space in video is defined as having three attributes. For example, one color space, RGB, uses the three primary colors, red, green and blue. Another color space uses luminance and color difference signals, or Y, Cr, Cb. HSV space defines color by its Hue, Saturation and Value (or brightness). Each of these color spaces contains colors that may not be reproducible in one of the other color spaces. When thinking of 4K/UHD video, many people may first think of its greater image resolution. But it can also produce a much wider range or gamut of colors than say HDTV video (Figure 9.12 (Plate 17)).

图 9.12（图 17） UHDTV 和 HDTV 的色域

Figure 9.12 (Plate 17) Color Gamuts for UHDTV and HDTV

注意在 ITU-R Recommendation BT.709 中概述了 HDTV 彩色视频的规范，通常简称为 Rec.709 或 BT.709。4K/UHDTV 彩色视频的规范在 ITU-R Recommendation BT.2020 中定义。

NOTE The specifications for HDTV color video are outlined in the ITU-R Recommendation BT.709, often referred to simply as Rec.709 or BT.709. The specifications for 4K/UHDTV color video are defined in the ITU-R Recommendation BT.2020.

钻石陈列

Diamond Display

图 9.13（图 18） 菱形显示

Figure 9.13 (Plate 18) Diamond Display

钻石显示是图像或图形是否在色域内的可靠且有用的指示器。如果信号延伸到菱形之外，则它超出了色域。如果它保持在色域内，则认为是合法的。在钻石显示器上识别色域的方式是通过代表颜色的简单矢量。这些向量一起形成两个菱形（图 9.13（图 18））。这些钻石之外的任何信号，或这种颜色 色域超出色彩空间限制，彩色监视器可能无法再现，或者如果信号转换为另一种格式，则可能无法正确转换。该显示用于确保信号的颜色部分不会过饱和。如果信号过饱和，菱形区域外的图像部分可能会被剪裁或限制为色域内的颜色。

The Diamond display is a reliable and useful indicator that an image or graphic falls within color gamut. If a signal extends outside the diamond, it is out of gamut. If it stays within the gamut, it is considered to be legal. The way the gamut is identified on the Diamond display is by simple vectors that represent colors. Together, these vectors form two diamond shapes (Figure 9.13 (Plate 18)). Any signal that is outside of these diamonds, or this color gamut, is outside the color space limits and may not be reproducible by a color monitor or may not translate properly if the signal is converted to another format. This display is used to ensure that the color portion of the signal is not oversaturated. If the signal is oversaturated, the portions of the image outside the diamond area may be clipped or limited to colors within the gamut.

使用范围进行调整

Making Adjustments Using Scopes

在对视频信号进行调整时，您会发现有一种调整顺序对设置电平最有效。首先对图像的亮度部分进行调整，一般先从黑色调整开始，然后是白色调整。然后，如有必要，进展到伽玛或中等水平。这个顺序的原因是调整相互作用。当您调整图像的暗部时，较亮的部分也会发生变化。对白色电平的调整也会影响图像的暗部，因此在继续进行伽马之前，请务必重新检查黑色电平。

When making adjustments to video signals, you will find that there is an order to adjustment that is most efficient to setting levels. Start by making adjustments first to the luminance part of the image, generally starting with the black adjustment first, followed by the white adjustment. Then, if necessary, progress to the gamma or middle levels. The reason for this order is that the adjustments interact. When you adjust the dark part of the image the brighter sections change as well. Adjustments to the white levels can also influence the dark part of the images, so be sure to recheck the black level before you move on to the gamma.

调整亮度后，您可以继续进行颜色调整。根据您使用的设备或程序，有几种不同的技术。您从哪个控件开始并不重要，但与亮度一样，存在交互和重叠，因此在您使用这些工具的过程中不断检查您之前的颜色选择非常重要。

After adjusting the luminance you can move on to color adjustments. Depending on the device or program you are using, there are several different techniques for this. Which control you start with is not important, but like luminance, there is interaction and overlap so it’s important to keep checking back with your earlier color choices as you progress through the tools.

许多图像专业人士区分颜色校正和颜色分级。通常为产生尽可能最好的、技术上正确的图像而进行的调整被认为是色彩校正。当使用调整来给镜头一种感觉时或颜色处理以增强故事讲述或引发情感，这些变化通常被称为颜色等级。将其视为高质量视频科学与作为创意工具的色彩艺术之间的界限。

Many image professionals make a distinction between Color Correction and Color Grading. Generally adjustments made to produce the best possible, technically correct image are considered color correction. When adjustments are used to give a shot a feel or color treatment to enhance story telling or elicit emotion, the changes are often referred to as the color grade. Think of it as the line between the science of good quality video and the art of color as a creative tool.

内置数字示波器显示器

Built-In Digital Scope Displays

用于视频制作的监视器通常在其显示器中内置了可以打开和关闭的示波器功能。这对于现场监听特别方便，因为它减少了制作人员需要携带的装备数量。图 9.14显示了一家制造商的监视器及其可用的数字显示器类型。

Monitors built for video production often have scope functions built into their displays that can be switched on and off. This is especially handy for field monitors, as it reduces the amount of gear that a production crew needs to carry. Figure 9.14 shows one manufacturer’s monitor and the type of digital displays it makes available.

图 9.14 内置数字示波器显示

Figure 9.14 Built-In Digital Scope Display

模拟和数字编码

Analog and Digital Encoding

编码或处理视频信号有四种主要方法。在模拟和数字域中，都有可用的分量输出和复合信号。虽然它们在每个领域中的引用方式相同，但模拟处理与数字处理不同，因此产生了四种不同的视频信号处理方式。它们是模拟复合、模拟分量、数字复合和数字分量。原来，所有的电视广播是模拟复合的。随着数字处理的出现，广播已经数字化。当数字广播成为标准时，大部分信号处理都转向了数字分量。

There are four major ways to encode or process video signals. In both the analog and digital domains, there are component outputs and composite signals available. While they are both referred to the same way in each domain, the processing is different for analog than it is for digital, thus yielding four distinct ways to process video signals. They are analog composite, analog component, digital composite, and digital component. Originally, all television broadcasting was analog composite. With the advent of digital processing, broadcasting has become digital. When digital broadcasting became the standard, the majority of signal processing shifted to digital component.

模拟编码过程

Analog Encoding Process

如上所述，有不同的方式来编码信号。NTSC 颜色处理是一种编码形式。例如，当颜色被添加到黑白信号时，该信息被编码以适合现有的传输和记录系统。这是使用毕达哥拉斯定理完成的（图 10.1）。

As mentioned above, there are different ways to encode a signal. The NTSC color process is one form of encoding. As an example, when color was added to the black and white signal, that information was encoded so it would fit within the existing transmission and recording systems. This was done using the Pythagorean theorem (Figure 10.1).

图 10.1 勾股定理

Figure 10.1 Pythagorean Theorem

勾股定理是平面几何中的一个方程，它指出如果已知直角三角形（包含 90º 角的三角形）的两条边，则第三条边的长度可以是 计算。其数学公式为 a ² + b ² = c ²。在NTSC视频信号中，绿色占亮度信号的59%，红色占30%亮度，蓝色占11%亮度。当红色和蓝色信号组合在一起时，它们包含的亮度信息少于单独的绿色。因此，如果将红色和蓝色信号定时为彼此相隔 90º，则可以从数学上推导出三角形的第三条边（绿色），从而消除绿色信号（图 10.1 ）。该编码信号中的视频颜色信息因此减少或压缩了一半以上。

The Pythagorean theorem is an equation in plane geometry that states that if the two sides of a right triangle (a triangle that contains a 90º angle) are known, the length of the third side can be calculated. The mathematical formula for this is a² + b² = c². In the NTSC video signal, green is 59% of the luminance signal, red is 30% luminance, and blue is 11% luminance. When the red and blue signals are combined, they contain less luminance information than green alone. Therefore, if the red and blue signals are timed to appear 90º apart from each other, the third side of the triangle (green) can be mathematically derived, thereby eliminating the green signal (Figure 10.1). The video color information in this encoded signal is thereby reduced or condensed by more than half.

亮度是通过在记录和传输过程中调制载波频率来编码的。光或亮度信息被转换为电信号，然后用于改变或调制载波信号。光信息也被转换为用于记录目的的磁和光数据，这是编码信号的附加形式。

Luminance is encoded by modulating a carrier frequency in both the recording and transmitting process. The light or luminance information is converted to electrical signals that are then used to change or modulate a carrier signal. Light information is also converted to magnetic and optical data for recording purposes, which are additional forms of encoded signals.

模拟复合信号

Analog Composite Signal

在模拟领域，有两种类型的信号处理：复合和分量。复合信号是构成视频信号的所有元素的组合。该信息包括亮度 (Y)、色差信号（RY、BY）和同步信息（H、V 和颜色）。该信息作为一个信号被记录和回放（图 10.2). 创建复合模拟信号是为了减少摄像机捕获的信息量，从而使彩色视频和同步信号能够适应黑白广播信号的带宽。组合所有信号的过程既降低了图像质量，又引入了肉眼可见的错误或伪影。复合模拟视频是四种常见编码中质量最低的。然而，它仍然经常出现在设备上，因为在许多显示器、媒体播放器和游戏机上，熟悉的黄色连接器都标有“视频”字样。

In the analog domain, there are two types of signal processing: composite and component. The composite signal is the combination of all the elements that make up the video signal. This information includes luminance (Y), the color difference signals (R-Y, B-Y), and synchronizing information (H, V, and color). This information is recorded and played back as one signal (Figure 10.2). Composite analog signals were created to reduce the amount of information captured by the camera to allow the color video and sync to fit into the bandwidth of a black and white broadcast signal. The process of combining all the signals both reduces the quality of the image and introduces errors, or artifacts, that can be seen visually. Composite analog video is the lowest quality of the four common encodings. It is often still found on equipment, however, as the familiar yellow connector labeled “video” on many displays, media players and game consoles.

图 10.2 模拟复合输入/输出

Figure 10.2 Analog Composite Input/Output

模拟分量信号

Analog Component Signal

在模拟分量系统中，亮度和色度信号是分开处理的。一些设备使用原始的红色、绿色和蓝色通道来执行此操作。同步可以在第四条线路或路径上进行，或者它可以是绿色信号的一部分。模拟计算机监视器使用具有五个信号的变体。红色、绿色和蓝色伴随着两条同步路径，水平同步和垂直同步各一条。计算机标准 VGA 使用这种格式，信号通常也是通过这种格式到达投影仪的。当您看到对 RGB、RGBS、RGBHV、“3 线”、“四线”或“五线”的引用时，您可以期待模拟分量信号。

In the analog component system, the luminance and chrominance signals are processed separately. Some devices do this with the original red, green and blue channels. Sync may be carried on a fourth wire or path, or it may be part of the green signal. Analog computer monitors use a variation with five signals. Red, green and blue are accompanied by two sync paths, one each for horizontal sync and vertical sync. The computer standard VGA uses this format and it is frequently how signals get to projectors. When you see references to RGB, RGBS, RGBHV, “3 wire,” “four wire,” or “five wire,” you can expect an analog component signal.

第二种形式的模拟分量使用来自前面讨论的复合编码过程的色差信号。然而，Y、RY 和 BY 并没有将这三者混合成单一的复合物，而是通过三根单独的导线通过系统。在大型设施中，这使用起来有点麻烦，因为每个设备都需要三个完整路径来传输信号。因此，接线架、路由切换器和处理设备需要三倍的空间和电力才能运行（图 10.3）。

A second form of analog component uses the color difference signals from the composite encoding process discussed earlier. However, instead of mixing the three resulting into a single composite, the Y, R-Y and B-Y are carried through the system on three separate wires. In a large-scale facility this is a bit cumbersome to work with, as each device needs three full paths to carry the signal. As a result, patch bays, routing switchers and processing equipment need three times the space and power to operate (Figure 10.3).

图 10.3 模拟和数字分量输入/输出

Figure 10.3 Analog and Digital Component Input/Output

保持元素分离的优点是可以保持更高质量的图像。通过以这种方式记录，需要更少的编码和解码，从而减少保真度损失并保留原始质量。

The advantage of keeping the elements separate is that a higher quality of image can be maintained. By recording in this manner, less encoding and decoding is required, thus reducing the loss of fidelity and retaining the original quality.

数字编码过程

Digital Encoding Process

编码用于数字域以实现与模拟相同的目的，即减少传输和记录的带宽。数字编码是将模拟信息转换为数字数据的过程。使用模数转换，可以将大量模拟信息简化为数字数据流。

Encoding is used in the digital domain to accomplish the same purposes as in analog, i.e., reduce the bandwidth for transmission and recording. Digital encoding is the process of converting analog information to digital data. Using analog to digital conversion, a very large amount of analog information can be reduced to a stream of digital data.

随着数字技术的出现，数字域中对色差信号的引用发生了变化。RY、BY的模拟符号改为PbPr，表示模拟信号的编码和传输（图10.4）。

With the advent of digital, the reference to the color difference signals in the digital domain was changed. The analog notation of R-Y, B-Y was changed to PbPr to indicate encoding and transferring of analog signals (Figure 10.4).

图 10.4 模拟输出

Figure 10.4 Analog Out

用于在数字域内编码和传输色差信号的符号记为 CbCr。虽然最初的名称 RY 和 BY 被名称 Pb 取代 和 Pr，随着数字视频的出现，这些随后被 Cb 和 Cr 所取代（图 10.5）。当提到模拟分量信号时，Pb 和 Pr 仍在使用。

The notation used for encoding and transferring the color difference signals within the digital domain is written as CbCr. While the original designations R-Y and B-Y were replaced by the designations Pb and Pr, with the advent of digital video, these were then replaced by Cb and Cr (Figure 10.5). Pb and Pr are still in use when referring to analog component signals.

图 10.5 分量视频输出

Figure 10.5 Component Video Out

数字复合信号

Digital Composite Signal

虽然不再是一种通用格式，但在 1990 年代数字电视设备首次出现时，数字复合信号被设计为一种过渡格式。它允许现有的电视设施开始向数字过渡，而无需完全重新设计。由于 HDTV 不支持此格式，因此仅供参考。数字复合视频与复合模拟视频非常相似，唯一的区别是信息是作为数字数据而不是模拟波形记录、存储和传输的。数字复合信号需要完整的模拟视频信号，将其所有元素组合在一起，并以数字形式记录或传输它。

Although no longer a common format, digital composite signals were designed as a transitional format in the 1990’s when digital television equipment first started to appear. It allowed existing television facilities to start a transition to digital without the need to completely re-tool. As HDTV does not support this format, it is of historical note only. Digital composite video is very similar to composite analog, with the only difference being that the information is recorded, stored, and transmitted as digital data rather than analog waveforms. A digital composite signal takes the complete analog video signal, with all of its elements combined, and records or transmits it in a digital form.

数字分量信号

Digital Component Signal

这是最常用的视频信号编码方法。大多数相机和图像创建设备都处理数字组件。数字分量视频采用构成视频信号 (YCbCr) 的元素，并在记录和传输时将它们分开。这在处理这些元素的方式上类似于模拟组件。

This is the most common method of video signal encoding. The majority of cameras and image creation devices process in digital component. Digital component video takes the elements that comprise a video signal (YCbCr) and keeps them separate in recording and transmission. This is similar to analog component in the way these elements are treated.

数码相机和记录设备的输入和输出可以是 RGB 或 YCbCr 分量。能够创建或复制这些数字元素的设备将为这些元素中的每一个元素提供单独的路径。尽管信号是分开的，但在数字世界中它们可以组合在一根电缆上。数字处理甚至允许将音频信号混合或多路复用到数据中。数据流还可以携带其他信息，例如控制信号和元数据（元数据将在第 17 章中讨论）。使用数字分量信号的设备连接的两种最常见方式是通过标记为 SDI 或 HDSDI 的同轴电缆和使用 HDMI 的消费类连接器（图 10.6（图 19））。

The inputs and outputs from digital cameras and recording devices can either be RGB or the YCbCr components. Equipment that is capable of creating or reproducing these digital elements will have separate paths for each of these elements. Although the signals are separate, in the digital world they can be combined on a single cable. Digital processing even allows the audio signals to be mixed or multiplexed into the data as well. The data stream can also carry other information such as control signals and metadata (metadata will be discussed in Chapter 17). The two most common ways equipment using digital component signals connects is via a coaxial cable labeled SDI or HDSDI and on a consumer connector using HDMI (Figure 10.6 (Plate 19)).

转码

Transcoding

因为存在多种标准和许多不同的视频设备，所以有时需要将一种类型的编码视频信号转换为另一种类型的编码视频信号。此过程称为转码。例如，数字分量信号可以转码为模拟复合信号或分量信号

Because there are several standards and many different video devices, it is necessary at times to translate from one type of encoded video signal to another type of encoded video signal. This process is known as transcoding. For example, a digital component signal can be transcoded to an analog composite or component

图 10.6（图 19） 数字组件连接

Figure 10.6 (Plate 19) Digital Component Connections

信号，反之亦然。由摄像机生成的 RGB 视频信号可以转码为模拟或数字分量 YPbPr 或 YCbCr 视频信号以供输入或输出。

signal, or vice versa. An RGB video signal, which is generated by a video camera, can be transcoded into an analog or digital component YPbPr or YCbCr video signal for input or output.

在编辑阶段也使用转码过程。媒体可能已经以一种格式（例如 HD）捕获和编辑，但可能需要转换为不同的格式才能在其目的地（例如 Web 或移动设备）上很好地播放（格式将更详细地讨论在第 19 章）。

The process of transcoding is also used during the editing stage. Media may have been captured and edited in one format, such as HD, but may need to be converted to a different format in order to play well at its destination, such as the web or on a mobile device (formats are discussed in more detail in Chapter 19).

编码和压缩

Encoding and Compression

信号编码是记录和传输过程的一个方面。虽然它允许对信号进行一些压缩，但其主要目的是促进这些信号的记录和传输。编码过程包含信号压缩的元素，但与数字域中的压缩过程不同（第14 章更详细地讨论了压缩）。

Signal encoding is an aspect of the recording and transmission process. While it allows for some compression of the signals, its main purpose is to facilitate the recording and transmission of these signals. The encoding process contains elements of signal compression, but is not the same as the compression process in the digital domain (compression is discussed in more detail in Chapter 14).

模拟域

Analog Domain

图 11.1 正弦波

Figure 11.1 Sine Wave

在本书的引言中，我们说过视觉和听觉是对能量波的反应，是一种模拟现象。视频 最初是作为模拟世界的一部分开发的。因为该系统是模拟的，所以它具有适应自然物理系统的便利和优势。然而，它也带来了所有的干扰和噪音问题。正如视频和音频一样，噪声是模拟信息。消除模拟视频信号中的噪声和干扰并不容易，因为它们采用与视频和音频信号相同的形式。此外，出于创造性目的操纵模拟信息也很复杂。

In the Introduction of this book, we said that sight and hearing are responses to energy waves, which is an analog phenomenon. Video was originally developed as part of the analog world. Because the system was analog, it had the ease and advantages of fitting into the natural physical system. However, it also carried with it all the interference and noise problems. Noise is analog information just as video and audio are. Getting rid of noise and interference in the analog video signal is not easy, as they take the same form as the video and audio signals. Also, manipulating analog information for creative purposes is complex.

为了消除干扰问题并更好地创造性地使用视频，创建了视频信号数字化过程。数字化是指将模拟信息转换为一系列数字。作为数字信息，信号不受现实世界的模拟干扰。数字化后，现实世界的物理问题对电视信号没有影响。这些引人注目的优势推动了向数字信号处理的转变。然而，作为人类，我们体验到的世界本质上是模拟的。因此，所有数字处理都必须从模拟转换开始，并以返回模拟结束。

To eliminate interference problems and make better creative use of video, a process of digitizing video signals was created. Digitizing refers to converting the analog information to a series of numbers. As digital information, the signals are not subject to real-world analog interference. Real-world physical problems have no effect on the television signal when it is digitized. These compelling benefits drove the move to digital signal processing. However, as humans, we experience the world as inherently analog. Therefore, all digital processing must start by converting from analog and end by going back to analog.

数字王国

Digital Domain

要创建数字视频，必须创建模拟正弦波的数字表示；也就是说，必须以数字方式重新创建模拟正弦波。为此，开发了一种在不同时间测量正弦波并为每次测量分配数值的过程。正弦波曲线随时间不断变化。因此，进行这种测量的频率越高，正弦波的数字再现就越准确。每天测量一次患者体温的医生可能无法非常准确地了解患者的状况。然而，每小时进行一次读数将使医生更清楚地了解患者的进展情况。

To create digital video, a digital representation of the analog sine wave had to be created; that is, the analog sine wave had to be recreated digitally. To do this, a process was developed to measure the sine wave at different times and assign a numerical value to each measurement. A sine wave curve is constantly changing over time. Therefore, the more frequently this measurement is taken, the more accurate the digital reproduction of the sine wave will be. A doctor measuring a patient’s temperature once a day might not get a very accurate picture of the patient’s condition. However, taking a reading every hour will give the doctor a much clearer idea of the patient’s progress.

采样率

Sampling Rate

考虑数字化的另一种方法是想象一个连点谜题。连接的点越多，曲线和轮廓就越能再现画面。点的频率，或医生的温度读数，被称为采样率。如果每隔 90º 测量正弦波，就会出现三条直线而不是曲线。然而，如果将采样率增加到每 10º、5º 甚至每 1º，则正弦波曲线将更准确地表示（图 11.2）。

Another way to think of digitizing is to imagine a connect-the-dots puzzle. The more dots there are to connect, the more closely the curves and outlines will reproduce the picture. The frequency of the dots, or the doctor’s temperature readings, are referred to as the sampling rate. If the sine wave was measured every 90º, there would be three straight lines instead of a curve. However, if the sampling rate was increased to every 10º, 5º, or even every 1º, the curve of the sine wave would be more accurately represented (Figure 11.2).

图 11.2 从抽样中确定的模式

Figure 11.2 Patterns Determined from Sampling

有两个因素会影响如何确定数字视频的采样率。首先，采样必须足够频繁地发生以准确地再现模拟信号。第二， 过程必须足够简单，以便与现有的模拟系统集成。满足这两个因素的一个因素是副载波频率的使用。副载波频率被用作采样率的基础，因为它是模拟视频系统的主要同步信号。

There were two factors affecting how the sampling rate for digital video was determined. First, the sampling had to occur frequently enough to accurately reproduce the analog signal. Second, the process had to be simple enough to integrate with the existing analog system. The one element that satisfied both factors was the use of the subcarrier frequency. The subcarrier frequency was used as the basis of the sampling rate because it was the main synchronizing signal for the analog video system.

然而，使用等于副载波频率的采样率并不能创建模拟信息的准确表示。为了从数字样本中准确地重建模拟信息，采样率必须是模拟信号中包含的最高频率的两倍以上，或者相反，被采样的频率必须小于采样频率的一半。

However, using a sampling rate that equals the subcarrier frequency does not create an accurate representation of the analog information. To accurately reconstruct the analog information from the digital samples, the sampling rate must be more than twice the highest frequency contained in the analog signals, or conversely, the frequencies being sampled must be less than half the sampling frequency.

这个结论是由贝尔实验室（原 AT&T）的工程师 Harry Nyquist 得出的，他在 20 年代中后期发表了有关电报传输速度的因素的论文。其他科学家 Karl Küpfmüller 和 Vladimir Kotelnikov 得出了与奈奎斯特相似的结论。后来，大约在 1948 年，工程师克劳德·香农 (Claude Shannon) 将奈奎斯特的工作应用于数字采样。因此，虽然这个采样频率规则可能有不同的名称，但它主要被称为 Nyquest 定理或 Nyquist-Shannon 采样定理。（在该标准之外工作而产生的错误称为混叠，即基于从不明确样本中得出的不正确数据创建的错误信号。）

This conclusion was derived by Harry Nyquist, an engineer at Bell Laboratories (originally AT&T), who in the mid to late 1920s published papers on factors concerning telegraph transmission speed. Other scientists, Karl Küpfmüller and Vladimir Kotelnikov, had come to a similar conclusion as Nyquist. And later, around 1948, an engineer, Claude Shannon, applied Nyquist’s work to digital sampling. So while this sampling frequency rule may be known by different names, it’s predominantly called either the Nyquest Theorem or the Nyquist-Shannon Sampling Theorem. (The error that is created by working outside this criterion is called aliasing, the creation of a false signal based on incorrect data derived from ambiguous samples.)

为了准确地表示视频信号中的模拟信息，决定使用副载波的倍数。决定的采样率是亮度信号副载波频率的四倍和颜色分量副载波频率的两倍。

To accurately represent the analog information in a video signal, it was decided that a multiple of the subcarrier should be used. The sampling rate decided on was four times the subcarrier frequency for the luminance signal and two times the subcarrier frequency for the color components.

将 3.58 兆赫（彩色副载波频率）乘以 4 的简单数学运算将得出 14.3 兆赫的采样率。为适应世界标准，数字分量信号的实际最终采样率亮度通道为 13.5 MHz，每个颜色通道为 6.75 MHz。为每个读数分配一个值，并记录该数字。记录的不是真实世界的模拟信号，而是代表信号被采样的每个瞬间的视频和音频电平的一系列数字。

Simple mathematics of multiplying 3.58 megahertz (color sub-carrier frequency) times 4 will give a sampling rate of 14.3 megahertz. To accommodate world standards, the actual final sample rate for digital component signals is 13.5 MHz for the luminance channel and 6.75 MHz for each color channel. A value is assigned to each reading, and that number is recorded. What is recorded is not a real-world analog signal, but a series of numbers representing video and audio levels at each instant the signal was sampled.

当视频信号变得高清时，需要更高的采样率来捕获更多的细节。在 HD 中，亮度采样率为 74.25 MHz，颜色分量以该速率的一半或 37.125 MHz 采样。每个新的更高分辨率图像都需要更高的采样率。4K 系统每行的信息量是原来的两倍，行数也是原来的两倍。因此，他们必须以比高清快 4 倍的速度对模拟世界进行采样。8K 图像系统必须将速率再提高 4 倍。

When video signals became High Definition, higher sample rates were needed to capture the greater detail. In HD, the luminance sample rate is 74.25 MHz and the color components are sampled at half that rate or 37.125 MHz. Each new higher resolution image requires a higher sample rate. 4K systems have twice the amount of information on each line, and twice as many lines. As a result they must sample the analog world 4x faster than HD. 8K image systems must up the rate again by another 4x.

在处理数字设备时，某些数字不断出现。例如 4:2:2、4:4:4 和 4:4:4:4。数字代表视频信号的数字采样标准。例如，4:2:2 表示信号亮度部分的副载波频率是采样率的四倍，每个色差信号的副载波频率是副载波频率的两倍。4:4:4 表示所有这三个信号的副载波频率的四倍，并且 4:4:4:4 添加键信号或 alpha 通道作为数字信息的一部分。虽然这些数字对于标清信号在数学上是准确的，但在谈论高清信号时也会保留它们。比率仍然存在，但与副载波频率不再有直接关系。

Certain numbers keep coming up when dealing with digital equipment. For example 4:2:2, 4:4:4, and 4:4:4:4. The numbers represent digital sampling standards for video signals. For example, 4:2:2 represents four times the subcarrier frequency as the sampling rate for the luminance portion of the signal, and two times the subcarrier frequency for each of the color difference signals. 4:4:4 represents four times the subcarrier frequency for all three of those signals and 4:4:4:4 adds the key signal, or alpha channel, as part of the digital information. While these numbers are mathematically accurate with Standard Definition signals, they are retained when talking about HD as well. The ratios remain, but there is no longer a direct relationship to the frequency of the subcarrier.

电脑处理

Computer Processing

早期的计算机使用一系列打开或关闭的开关来运行，提供是或否选项。这可以比作为找出某人的名字而创建的问卷，其中只能给出是或否的答案，每个答案分别由 0 或 1 表示。要给出一个人的名字，将提供一个字母表中的字母，然后这个人会说是或否，以表明该字母是否是他或她名字中的下一个字母。他们会检查字母表，让这个人对每个字母回答是或否，然后重复这个过程，直到全名拼写正确。这个过程会很慢但很准确。

Early computers functioned using a series of switches that were either on or off, providing either a yes or no option. This could be likened to a questionnaire created to find out someone’s name where only yes or no answers can be given, each answer represented by a 0 or 1, respectively. To give a person’s name, a letter from the alphabet would be offered and the person would say yes or no to indicate whether that letter is the next letter in his or her name. They would go through the alphabet with the person answering yes or no to each letter, then repeating the process until the full name was spelled correctly. The process would be slow but accurate.

这基本上就是计算机在处理其内存时所做的事情。它通过是和否问题的速度越快，它处理信息的速度就越快。处理此信息的速率以兆赫兹为单位，并且是因计算机而异的规格之一。以兆赫 (MHz) 为单位测量的速率越高，计算机处理器的速度就越快。

That is essentially what a computer is doing as it goes through its memory. The faster it goes through the yes and no questions, the faster it can process the information. The rate at which this information is processed is measured in megahertz and is one of the specifications that differs from computer to computer. The higher the rate as measured in megahertz (MHz), the faster the computer processor.

二进制系统

Binary System

上面提到的每个是或否的答案都由零或一，或零和一的组合表示。这称为二进制系统，因为它由两个数字组成。二进制系统用于所有数字化过程，因为它是计算机的语言。每个零和一个都是数字或二进制位。计算机一次可以读取的二进制或数字位数称为字长。最初的计算机处理器是 8 位（也称为字节），但很快发展到 16 位、32 位等。计算机继续提高其处理更大容量的能力单词大小。计算机可以处理的字数越大，它处理信息的速度就越快。计算机的处理速度也在以兆赫为单位继续增加。这两个因素的结合导致了计算机效率和速度的提高。

Each of the yes or no answers referred to above is represented by a zero or one, or combination of zeros and ones. This is called a binary system because it is made up of two numbers. The binary system is used for all digitizing processes because it is the language of computers. Each zero and one is a digital or binary bit. The number of binary or digital bits the computer can read at once is known as the word size. The original computer processors were 8-bit (also referred to as a byte), but soon grew to 16-bit, 32-bit, and so on. Computers continue to increase their capability of handling larger word sizes. The bigger the word size the computer can handle, the faster it can process information. The processing speed of computers continues to increase in megahertz as well. These two factors combined have been responsible for the increase in computer efficiency and speed.

与基于两个数字的二进制系统不同，当今使用的常见数学系统是十进制系统，它使用 0 到 9 的值。在这个系统中，最右边的列代表一个或单个单位，而左边的下一列代表几十个单位。左边第三列代表数百个单位，第四列代表数千个单位，依此类推。每列都有一个从 0 到 9 的值。在 9 之后，新列从左侧开始。例如，198 在个位列中表示为 8，在十位列中表示为 9，在百位列中表示为 1。198 之后是 199，然后是 200。200 表示有 2 个百单位、0 个十单位和 0 个单独单位。

Unlike the binary system, which is based on two numbers, the common mathematical system in use today is the decimal system, which uses values 0 through 9. In this system, the column on the far right represents ones, or individual units, and the next column to the left represents tens of units. The third column to the left represents hundreds of units, the fourth column represents thousands of units, and so on. Each column has a value from 0 to 9. After 9, a new column is started to the left. For example, 198 is represented as an 8 in the ones column, a 9 in the tens column, and a 1 in the hundreds column. After 198 comes 199 and then 200. A 200 means there are 2 hundreds of units, 0 tens of units, and 0 individual units.

表 11.1 二进制系统值

Table 11.1 Binary System Values

在二进制系统中，计算机执行相同类型的数学运算，但它的列只有 0 和 1 的值。第一列 代表一个或个别单位。左边的第二列代表两个单位。第三列代表四个单位。左边第四列代表八个单位，依此类推。

In the binary system, a computer does the same type of math but its columns only have values of 0 and 1. The first column represents ones or individual units. The second column to the left represents twos of units. The third column represents fours of units. The fourth column to the left represents eights of units, and so on.

使用上表，如果第二列中有一个 1，第一列中有一个 0，则表示有一个二进制单元。数字 3 由第一列中的 1 和第二列中的 1 表示，表示 1 个二元组加 1 个独立单元。数字 4 在第三列中为 1，在第一列和第二列中均为 0，表示 1 个四位单位和 0 个双位和个位单位。五由 1 个四位单位、0 个二位单位和 1 个单独单位或 101 表示。八列中的每一列中的 1 或 11111111 表示数字 255。数字 256 是第九列的开头。因此，8 位计算机一次可以处理的最大字是八位或一个字节。

Using the table above, if there is a 1 in the second column and a 0 in the first column this indicates there is one unit of twos. The number 3 is represented by a 1 in the first column and a 1 in the second column, indicating 1 unit of twos plus 1 individual unit. The number 4 is a 1 in the third column and a 0 in both the first and second columns, indicating 1 unit of fours and 0 units of twos and ones. Five is represented by 1 unit of fours, 0 units of twos, and 1 individual unit, or 101. A 1 in each of the eight columns, or 11111111, represents the number 255. The number 256 is the start of the ninth column. Thus, the largest word that an 8-bit computer can process at a time is eight bits or one byte.

样本量

Sample Size

抽样的第二个因素是每个样本可以携带多少信息。如果单个位用于采样，那只会指示是否存在信号，而绝不会代表其模拟值。如果使用更多位，则可以在样本中表示更准确的模拟值。例如，对于四位，模拟信号可以是 16 种不同电压中的任何一种。在视频中，每个样本通常使用 8 或 10 位。这会在每个样本中创建 256（使用 8 位）或 1024（使用 10 位）不同的级别。

A second factor in sampling is how much information each sample can carry. If a single bit is used for sampling, that would only indicate if there is a signal present or not, but would in no way represent its analog value. If more bits are used, more accurate analog values can be represented in the sample. For example, with four bits, the analog signal could be any one of 16 different voltages. In video, 8 or 10 bits are typically used for each sample. This creates either 256 (using 8 bits) or 1024 (using 10 bits) different levels at each sample.

人的听觉比视觉对样本量中的误差更敏感。因此，音频样本大小通常为每个样本 16 或 24 位。

Human hearing is more sensitive than vision to errors in the sample size. As a result, audio sample sizes are typically 16 or 24 bits per sample.

数字流

Digital Stream

一旦数据被数字化，就可以传输包含数据的数字位。用于数字数据的传输形式称为串行数字。术语串行是指作为一个连续的数字数据流或数字流发送的一系列二进制位。在处理视频信号时，此数字流包含有关图像和音频的所有信息。

Once data has been digitized, the digital bits that comprise the data can be transmitted. The form of transmission used for digital data is referred to as serial digital. The term serial refers to the series of binary bits that are sent out as one continuous stream of digital data, or the digital stream. When working with a video signal, this digital stream contains all the information about the image and audio.

数字流中的数据量决定了图像的质量或细节。图像中的细节（或采样信息）越多，数据量就越大（图 11.3）。数据量越大，传输数据所需的带宽量就越大。这种数据移动称为吞吐量。带宽越大——或吞吐量越大——串行数字流中可以承载的数据量就越大。如果用于传输的带宽对于数字流中承载的数据量而言太小，数字位就会丢失或丢失。结果是图像质量下降。在某些情况下，这会导致信号完全丢失。

The quantity of data in a digital stream dictates the quality or detail of the image. The more detail—or sampled information—from the image, the larger the quantity of data (Figure 11.3). The larger the quantity of data, the greater the amount of bandwidth required to transmit the data. This movement of data is referred to as throughput. The larger the bandwidth—or the greater the throughput—the greater the quantity of data that can be carried in the serial digital stream. If the bandwidth used for transmission is too small for the quantity of data being carried in the digital stream, digital bits are dropped or lost. The result is a loss of image quality. In some cases, this can result in a complete loss of the signal.

图 11.3 表示所取样本的二进制数

Figure 11.3 Binary Numbers Representing Samples Taken

为了正确接收和解释数字流，必须组织所有数字位。组织数字 数据类似于在一组句子中添加标点符号。如果没有标点符号，就很难或不可能阅读和理解材料。数字数据以位开始，以零和一的形式出现，它们被分组为称为帧的元素。帧组被组织成数据包。数据包组被组织成段。一组段的结果是数字流（图 11.4）。

In order for the digital stream to be received and interpreted correctly, all of the digital bits must be organized. Organizing digital data is similar to adding punctuation to a group of sentences. Without punctuation, it would be difficult or impossible to read the material and comprehend it. Digital data begins as bits, in the form of zeros and ones, which are grouped into elements called frames. Groups of frames are organized into packets. Groups of packets are organized into segments. The result of a group of segments is the digital stream (Figure 11.4).

图 11.4 数字流数据

Figure 11.4 Digital Stream Data

数字流中的每个元素都经过编码，因此可以按正确的顺序接收和组合。如果数字流中的某些信息从这些元素中的任何一个丢失，则数据或图像可能变得无法被接收源理解。除了源自一个来源的数据之外，串行数字流还可能包含来自多个其他来源的信息。正如一台计算机不是 Internet 上唯一的活跃参与者一样，传输各种类型数据的多个源可能共享一条传输线。正是出于这个原因，帧、数据包和段信息至关重要。没有这个数据，没有办法解码串行数字流以在预期的接收源处重新创建原始数据。

Each of these elements in the digital stream is encoded so it can be received and combined in the proper order. If some of the information from the digital stream is lost from any one of these elements, the data, or image, can become unintelligible to the receiving source. In addition to data originating from one source, a serial digital stream may also contain information from several other sources. Just as a single computer is not the only active participant on the Internet, several sources transmitting various types of data may share a single transmission line. It is for this reason that the frame, packet, and segment information is critical. Without this data, there is no way to decode the serial digital stream to recreate the original data at the intended receiving source.

串行数字接口

Serial Digital Interface

通过SDI或串行数字接口将数据从一个源传输到另一个源。此接口允许在源之间传输数据。SDI 有时是一个独立的设备，有时它作为一个设备的组成部分。SDI 输入/输出端口可以在摄像机、VCR 和其他制作和计算机设备上找到（图 11.5）。

The transfer of data from one source to another occurs through an SDI, or serial digital interface. This interface allows the transfer of data between sources. An SDI is sometimes a stand-alone device and sometimes it is incorporated as an integral part of a piece of equipment. An SDI input/output port can be found on cameras, VCRs, and other production and computer equipment (Figure 11.5).

与嵌入数字流中的视频信息一起的是所有音频信息——多达 16 个通道。没有单独的音频线。所有的视频和音频数据都包含在一个串行数字流中，并通过一根 SDI 电缆传输。

Along with the video information embedded in the digital stream is all the audio information—up to 16 channels. There are no separate wires for audio. All of the video and audio data is contained in a single serial digital stream and carried through a single SDI cable.

图 11.5 串行数字接口 (SDI)

Figure 11.5 Serial Digital Interface (SDI)

HDMI接口

HDMI Interface

另一个非常常见的用于传输数字信号的接口是 HDMI。这是消费相机、显示器和计算机上最常见的接口。虽然它不直接与 SDI 设备兼容，但廉价的转码器允许 HDMI 设备在专业环境中使用。由于 HDMI 信号被限制在 20 英尺左右，因此无法在大型演播室轻松使用。

Another very common interface for carrying digital signals is HDMI. This is the most common interface on consumer cameras, displays and computers. While it is not directly compatible with SDI equipment, inexpensive transcoders allow HDMI devices to be used in a professional environment. Because HDMI signals are limited to about 20 feet, they cannot be easily used in a large studio.

模拟标准

Analog Standards

NTSC 模拟是视频标准的一个例子。其他世界标准包括 PAL 和 SECAM。如图 12.1所示，每个标准都在许多不同的国家/地区使用。

NTSC analog is one example of a video standard. Other world standards include PAL and SECAM. As you can see in Figure 12.1, each standard is used in many different countries.

1941年，制定了第一个NTSC标准。并且在 1953 年，创建了一个包含彩色电视条款的新标准。因为还有那么多黑白接收器在使用，另一个

In 1941, the first NTSC standard was developed. And in 1953, a new standard with a provision for color television was created. Because there were still so many black and white receivers in use, another

图 12.1 世界标准地图

Figure 12.1 World Map of Standards

NTSC 标准于 1953 年采用，允许现有接收器与彩色电视广播之间的兼容性。NTSC 是第一个被广泛采用的广播彩色系统，直到 21 世纪的第一个十年才被数字标准取代，它一直占据主导地位。

NTSC standard was adopted in 1953 that allowed for compatibility between those existing receivers and color television broadcasting. NTSC was the first widely adopted broadcast color system and remained dominant until the first decade of the 21st century, when it was replaced with digital standards.

设定数字标准

Setting Digital Standards

与模拟标准 NTSC、PAL 和 SECAM 一样，数字标准是通过各种全球组织根据国际协议制定的，其中许多组织都在国际标准化组织 ISO 的支持下。这个非政府组织成立于 1947 年，由超过 165 个成员国组成，为科学、技术和经济活动制定技术标准。

Like the analog standards NTSC, PAL and SECAM, digital standards are set by international agreement through various worldwide organizations, many of which fall under the auspices of the ISO, the International Organization for Standardization. Established in 1947, this non-government organization, comprised of over 165 member countries, sets technical standards for scientific, technological, and economic activity.

ISO 赞助的一些视频组织包括 SMPTE、NTSC、EBU（欧洲广播联盟）和 ATSC（高级电视系统委员会）。ATSC 是一个国际非营利组织，成立于 1982 年，旨在制定数字电视的自愿性标准。ATSC 拥有大约 140 个成员，代表广播、广播设备、电影、消费电子、计算机、电缆、卫星和半导体行业。在制造商研究、开发和争夺播放、录制和广播数字视频的最佳方式的时候，设置所有制造商都可以遵守的标准。1995 年，ATSC 在一份简称为 A/53 的文件中定义并批准了数字电视标准。这包括标准清晰度电视 (SDTV) 和高清晰度电视 (HDTV)，这将在本章后面进行讨论。

Some of the video organizations under the auspices of the ISO include SMPTE, NTSC, EBU (European Broadcast Union), and the ATSC (Advanced Television Systems Committee). ATSC is an international non-profit organization formed in 1982 for the purpose of developing voluntary standards for digital television. The ATSC has approximately 140 members representing the broadcast, broadcast equipment, motion picture, consumer electronics, computer, cable, satellite, and semiconductor industries. At a time when manufacturers were researching, developing and vying for the best way to play, record and broadcast digital video, it was imperative to set a standard that all manufacturers could adhere to. In 1995, the ATSC defined and approved the Digital Television Standards in a document called simply A/53. This included standard definition television (SDTV) and high definition television (HDTV), discussed later in this chapter.

标准参数

Standards Parameters

在定义具体标准之前，有必要了解标准的基本参数。模拟电视标准有特定的标准，而 ATSC 推荐的数字电视标准允许各种参数的组合。用于定义标准的一些参数包括构成图像的像素数（图像分辨率）、图像的形状（纵横比）、构成图像的像素的形状（像素纵横比）、扫描用于显示图像的进程、音频和每秒显示的帧数（帧速率或 fps）。这些参数的特定组合称为标准格式。

Before defining specific standards, an understanding of the basic parameters of a standard is necessary. Analog television standards had specific criteria, while the ATSC’s recommended Digital Television Standard allows for a combination of various parameters. Some of the parameters used to define a standard include how many pixels make up the image (image resolution), the shape of the image (aspect ratio), the shape of the pixels that make up the image (pixel aspect ratio), the scanning process used to display the image, the audio frequency, and the number of frames displayed per second (frame rate or fps). A specific combination of these parameters is referred to as a standard format.

图像分辨率

Image Resolution

图像分辨率是在摄像机、视频监视器或其他显示源中创建或显示的视频图像的细节或质量。细节量由水平扫描线中的像素数（图像元素）乘以电视标准帧中的扫描线数。图像中的组合像素和线数表示所谓的空间密度分辨率，或构成一帧的总像素数。对于标清 ATSC 数字视频，图像分辨率为每行 720 像素，每帧有 480 条有效扫描线 (720 × 480)。

Image resolution is the detail or quality of the video image as it is created or displayed in a camera, video monitor, or other display source. The amount of detail is controlled by the number of pixels (picture elements) in a horizontal scan line multiplied by the Television Standards number of scan lines in a frame. The combined pixel and line count in an image represents what is known as the spatial density resolution, or how many total pixels make up one frame. For standard definition ATSC digital video, the image resolution is 720 pixels per line with 480 active scan lines per frame (720 × 480).

增加图像中的像素数量会增加细节量。这对应于图像分辨率的增加。如果显示的图像保持相同大小，则分辨率的增加会增加图像的细节。或者，可以将较高分辨率的图像显示得更大，同时保持与较低分辨率图像相同的细节程度。

Increasing the number of pixels in an image increases the amount of detail. This corresponds to an increase in the resolution of the image. If the displayed image is kept at the same size, an increase in resolution would increase the detail in the image. Alternatively, a higher-resolution image could be displayed much larger while keeping the same degree of detail as the lower-resolution image.

例如，如果在 21 英寸的显示器上显示 720 × 480 的图像，并且该图像的分辨率增加，则图像将具有更多细节。可以在更大的显示器上显示分辨率更高的同一图像，而不会丢失细节。

For example, if a 720 × 480 image is displayed on a 21-inch monitor, and the resolution of that image is increased, the image would have more detail. The same image with increased resolution could be displayed on a larger monitor with no loss of detail.

纵横比

Aspect Ratios

视频图像通常以矩形显示。为了描述图像的特定形状，将图像的宽度与其高度进行比较以得出其纵横比. 该比率描述图像的形状，与其大小或分辨率无关。视频中两种常见的纵横比是 16 × 9 和 4 × 3。例如，纵横比为 16 × 9 的图像的宽度为 16 个单位，高度为 9 个单位。实际比率不取决于任何特定的计量单位。如果一个 16 × 9 的图像或显示器有 16 英尺宽，那么它就是 9 英尺高。如果它是 16 英寸宽，它就是 9 英寸高。9 码高的显示器将是 16 码宽。想想那种尺寸的体育场记分牌。较旧的标准清晰度显示器更接近正方形。4 英尺宽乘 3 英尺高的显示器称为 4 × 3 比例。

Video images are generally displayed in a rectangular shape. To describe the particular shape of an image, the width of the image is compared to its height to come up with its aspect ratio. This ratio describes the shape of the image independent of its size or resolution. Two common aspect ratios in video are 16 × 9 and 4 × 3. An image with a 16 × 9 aspect ratio would be, for example, 16 units across and 9 units tall. The actual ratio does not depend on any particular unit of measure. If a 16 × 9 image or display were 16 feet wide, it would be 9 feet tall. If it were 16 inches wide, it would be 9 inches tall. A display that is 9 yards tall would be 16 yards wide. Think of a stadium scoreboard at that size. Older standard definition displays were a bit closer to square. A display that is 4 feet wide by 3 feet tall would be referred to as a 4 × 3 ratio.

另一种记录纵横比的常用方法是用图像的长度除以高度。在 16 × 9 的示例中，当宽度 16 除以高度 9 时，结果将为 1.777777 个单位长。这通常四舍五入为 1.78 并表示为 1.78 比 1，或显示为 1.78:1 的比率。对于每个高度单位，我们需要 1.78 个宽度单位。较旧的 4 × 3 标准清晰度图像为 1.33:1。当四除以三时，结果为 1.33333333。

Another common way to note aspect ratio is to divide the length of the image by the height. In the 16 × 9 example, when the width amount of 16 is divided by the height of 9, the result would be 1.777777 units long. This is often rounded to 1.78 and expressed as 1.78 to 1, or shown as the ratio 1.78:1. For each unit of height we need 1.78 units of width. The older 4 × 3 standard definition image would be 1.33:1. When four is divided by three the result is 1.33333333.

电影界使用许多不同的图像比例，但它们几乎总是表示为与 1 个高度单位的比较。例如，在 Cinemascope 中放映的影院上映电影的纵横比为 21 × 9，但通常称为 2.35:1。另一种常见的电影纵横比是 1.85:1，更接近高清的 16×9 纵横比（图 12.2）。

The film world uses a number of different image ratios, but they are almost always expressed as comparisons to 1 unit of height. For example, a theatrical release movie, showing in Cinemascope, has an aspect ratio of 21 × 9, but it is more commonly referred to as 2.35:1. Another common film aspect ratio is 1.85:1, which is closer to the 16 × 9 aspect ratio of HD (Figure 12.2).

像素纵横比

Pixel Aspect Ratio

像素纵横比是像素本身的大小和形状。在计算机显示器中，像素是长宽比为 1 比 1 的正方形。NTSC 像素的长宽比为 0.91:1，这使得它们又高又薄。在设置 NTSC 视频图像数字化标准时，目的是在最高实用分辨率下对图像进行数字化。虽然水平扫描线中的像素数量可以设置为任意数量，但扫描线的数量不能任意增加，因为它们是 NTSC 标准的一部分。因此，像素被更改为窄的垂直矩形，从而增加了每行的像素数量并增加了图像分辨率。

The pixel aspect ratio is the size and shape of the pixel itself. In computer displays, pixels are square with an aspect ratio of 1 to 1. NTSC pixels have an aspect ratio of 0.91:1, which makes them tall and thin. When setting the standard for digitizing the NTSC video image, the intent was to digitize the image at the highest practical resolution. While the number of pixels in a horizontal scan line could be set to any amount, the number of scan lines could not be arbitrarily increased since they are part of the NTSC standard. Therefore, the pixels were changed to a narrow, vertical rectangle shape, allowing an increase in the number of pixels per line and added image resolution.

在数字世界中，有时会更改像素的纵横比以在每行上获取更少的样本。（请记住，水平扫描线中的像素数可以设置为任意数量，

In the digital world, the aspect ratio of the pixels is sometimes changed to take fewer samples on each line. (Remember, the number of pixels in a horizontal scan line can be set to any amount,

图 12.2 纵横比

Figure 12.2 Aspect Ratios

但扫描线的数量不能任意增加，因为它们是现有标准的一部分。）虽然扩展每个像素的宽度减少了存储和发送的数据量，但它也降低了水平分辨率。例如，相机可能有一个 1920 × 1080全光栅传感器，这意味着传感器本身是全尺寸和矩形的——它实际上是 1920 × 1080，像素纵横比是正方形或 1:1。但是，有些记录格式不是全光栅的。通过将每个像素的宽度扩展到 1.33:1 的纵横比，可以以 1440 x 1080 的分辨率再现 1920 × 1080 的高清图像。这样可以节省大约三分之一的必须存储或传输的数据量。1440 × 1080 图像被称为细光栅格式（图 12.3）。

but the number of scan lines cannot be arbitrarily increased since they are part of an existing standard.) While expanding the width of each pixel reduces the amount of data being stored and sent, it also reduces horizontal resolution. For example, a camera may have a sensor that is 1920 × 1080 full raster, meaning that the sensor itself is full-sized and rectangular—that it is in fact 1920 × 1080, and the pixel aspect ratio is square or 1:1. However, there are recording formats that are not full raster. By expanding the width of each pixel to an aspect ratio of 1.33:1, the HD 1920 × 1080 image can be reproduced at 1440 x 1080. This saves about a third on the amount of data that has to be stored or transmitted. The 1440 × 1080 image is referred to as a thin raster format (Figure 12.3).

图 12.3 全光栅帧和精简光栅帧大小

Figure 12.3 Full and Thin Raster Frame Sizes

隔行扫描和逐行扫描模式

Interlace and Progressive Scan Modes

隔行扫描是将一帧视频分成两个场的过程。一个视频场包含信息的奇数行，而另一个包含扫描图像的偶数行。回放时，两个场交错在一起，形成一个完整的视频帧。

Interlace scanning is the process of splitting a frame of video into two fields. One field of video contains the odd lines of information while the other contains the even lines of the scanned image. When played back, the two fields are interlaced together to form one complete frame of video.

在历史上电视使用隔行扫描过程的地方，计算机使用非隔行扫描或逐行扫描技术。计算机图像屏幕可以每秒刷新 72 次。因为这个速率比视觉的暂留速度更快，所以消除了闪烁问题。因此，不需要将帧分成两个场。相反，图像是从上到下逐行扫描的，没有使用隔行扫描过程。每次扫描图像时都会捕获或复制完整的帧（图 12.4）。

Where historically television used an interlace scanning process, the computer uses a non-interlaced or progressive scanning technique. Computer image screens can be refreshed as rapidly as 72 times a second. Because this rate is faster than the persistence of vision, the problem of flicker is eliminated. Therefore, there is no need to split the frame into two fields. Instead, the image is scanned from top to bottom, line by line, without using an interlacing process. The complete frame is captured or reproduced with each scan of the image (Figure 12.4).

逐行扫描的图像比等效的隔行扫描图像具有更明显的细节清晰度。逐行扫描的图像包含完整的视频帧，而隔行扫描帧包含两个时刻的图像，每个图像的分辨率都是全帧的一半。

Progressively scanned images have greater apparent clarity of detail than an equivalent interlaced image. The progressively scanned image holds a complete frame of video, whereas an interlaced frame contains images from two moments in time, each at half the resolution of the full frame.

计算机行业一直坚持比电视行业使用的图像更详细、质量更高的图像。计算机图像通常需要非常精细的细节，并且通常包含大量在标准电视屏幕上无法阅读的文本。传统的电视图像不需要像计算机信息那样的详细程度。在数字环境中，限制因素是有足够的带宽来传输信息。隔行扫描允许在分配给信号传输的有限空间频谱中传输更多信息。

The computer industry has always insisted on a far more detailed and higher quality image than has been used in the television industry. Computer images usually require very fine detail and often include a great deal of text that would be unreadable on a standard television screen. Traditional television images did not require the same degree of detail as computer information. In a digital environment, the limiting factor is enough bandwidth to transmit the information. Interlace scanning allowed more information to be transmitted in the limited spectrum of space allotted for signal transmission.

图 12.4 (A) 隔行扫描和 (B) 逐行扫描

Figure 12.4 (A) Interlaced Scanning and (B) Progressive Scanning

在列出特定标准的标准时，扫描模式是隔行还是逐行的指示在行数之后显示为“i”或“p”，例如 480p、720p、1080i 等。

When listing the criteria for a particular standard, the indication of whether the scanning mode is interlaced or progressive appears as an “i” or “p” following the line count, such as 480p, 720p, 1080i, and so on.

帧率

Frame Rate

无论像素数或行数如何，帧速率都是每秒扫描的完整帧数。该速率表示所谓的图像时间分辨率，或图像扫描的快慢程度。帧速率因速率而异捕获或创建的图像，使用视频图像的系统的需求或能力，以及系统再现图像的能力。

The frame rate, regardless of the pixel or line count, is the number of full frames scanned per second. This rate represents what is known as the temporal resolution of the image, or how fast or slow the image is scanned. Frame rates vary depending on the rate at which the image was captured or created, the needs or capability of the system using the video image, and the capability of the system reproducing the image.

例如，图像可能以每秒 24 帧 (fps) 的速度捕获，以 29.97 fps 的速度编辑，并以 30 fps 的速度再现。帧速率的每次变化都表示不同的格式。不同的帧速率包括 23.98、24、25、29.97、30、59.94 和 60 fps。在将颜色添加到 NTSC 信号之前，黑白视频以每秒 30 帧或 30 fps 的速度扫描。当向信号添加颜色时，扫描速率必须略微降低至 29.97 fps 以适应额外的颜色信息。曾经在 NTSC 中广播的国家仍然使用该遗留费率，以促进合并以前录制的旧材料。不需要广播版本的项目可以使用最适合源材料的整数或非十进制速率（24、25、30 或 60 fps）。

For example, an image may have been captured at 24 frames per second (fps), edited at 29.97 fps, and reproduced at 30 fps. Each change in the frame rate would denote a different format. Different frame rates include 23.98, 24, 25, 29.97, 30, 59.94, and 60 fps. Before color was added to the NTSC signal, black and white video was scanned at 30 frames per second, or 30 fps. When color was added to the signal, the scanning rate had to be slowed down slightly to 29.97 fps to accommodate the additional color information. That legacy rate is still used in countries that once broadcast in NTSC to facilitate incorporation of older previously recorded material. Projects that do not require a broadcast version can use the integer, or non-decimal rate (24, 25, 30, or 60 fps), that is best suited to the source material.

传统清晰度电视 (CDTV)

Conventional Definition Television (CDTV)

在创建数字视频标准时，ATSC 重新定义了之前已经在使用的标准。全世界使用的模拟标准被归入一个新定义的类别，称为常规清晰度电视或 CDTV。CDTV 是指所有原始的模拟电视标准。

When digital video standards were created, the ATSC redefined the prior standards that were already in use. The analog standards used throughout the world were placed in a newly defined category called Conventional Definition Television, or CDTV. CDTV refers to all the original analog television standards.

在 NTSC 系统中，CDTV 标准图像分辨率为 640 像素乘以 480 线活动视频。帧速率为每秒 29.97 帧，有两个隔行扫描场，每个场包含 240 行活动视频。PAL 标准图像分辨率为 760 像素 x 580 行。PAL 帧速率为 25 fps，有两个隔行扫描场，每个场包含 288 行活动视频。SECAM也有 每行 760 像素和 580 行，与 PAL 共享相同的帧速率和扫描模式（表 12.1）。

In the NTSC system, the CDTV standard image resolution is 640 pixels by 480 lines of active video. The frame rate is 29.97 frames per second with two interlaced fields, each containing 240 lines of active video. The PAL standard image resolution is 760 pixels by 580 lines. The PAL frame rate is 25 fps with two interlaced fields, each containing 288 lines of active video. SECAM also has 760 pixels per line and 580 lines, and shares the same frame rate and scan mode as PAL (Table 12.1).

表 12.1 CDTV 标准

Table 12.1 CDTV Standards

在最初的模拟标准中，每个单独的标准都包含自己的处理颜色信息的方法。随着数字视频标准的出现，颜色编码被重新定义为一个名为 CCIR 601 的新国际标准，该标准以首先制定该标准的法国组织国际无线电咨询委员会命名。颜色编码过程的进一步完善以及 CCIR 与其他组织的合并导致名称从 CCIR 601 更改为以国际电信联盟命名的 ITU-R 601。

In the original analog standards, each individual standard contained its own method for processing color information. With the advent of digital video standards, color encoding was redefined to a new international standard called CCIR 601, named after the French organization Consultative Committee on International Radio, which first developed the standard. Further refinement of the color encoding process and the merger of the CCIR with other organizations led to a change in name from CCIR 601 to ITU-R 601 named after the International Telecommunications Union.

数字电视类别 (DTV)

Digital Television Categories (DTV)

数字电视类别或 DTV 是从数字视频领域发展而来的，涵盖了所有数字视频标准。它有两个子类别：标准清晰度电视(SDTV) 和高清晰度电视 (HDTV)。为了进一步划分 DTV 类别，存在称为 EDTV 或增强清晰度电视的中间标准。

The Digital Television category, or DTV, developed from the growth of the digital video domain and encompasses all digital video standards. It has two subcategories: Standard Definition Television (SDTV) and High Definition Television (HDTV). To further divide the DTV category, there is an in-between standard referred to as EDTV, or Enhanced Definition Television.

数字电视标准

Digital Television Standards

如前所述，1995 年，ATSC 为美国电视信号的数字广播制定了一套称为 A/53 的标准。这些标准使用 MPEG-2 压缩方法进行视频压缩（有关 MPEG 压缩的更多信息，请参阅第 15 章）。AC-3 杜比数字标准（文件 A/52）虽然在 MPEG-2 标准之外，但已在美国被采纳为数字电视音频标准（有关数字音频的更多信息，请参见第 16 章）。

As mentioned earlier, in 1995, the ATSC created a set of standards, known as A/53, for digital broadcasting of television signals in the United States. These standards use the MPEG-2 compression method for video compression (see Chapter 15 for more information on MPEG compression). The AC-3 Dolby Digital standard (document A/52), although outside the MPEG-2 standard, has been adopted in the United States as the standard for Digital TV audio (see Chapter 16 for more information on digital audio).

ATSC 制定的标准被美国联邦通信委员会 (FCC) 采用。但是，由于来自计算机行业的压力，下表所示的标准（表 12.2 ）被 FCC 否决了。当时的想法是将使用何种标准的选择权留给市场，只要它适用于 MPEG-2 压缩方案即可。结果是所有制造商和广播公司都在使用 ATSC 表中包含的标准。

The standards created by the ATSC were adopted by the Federal Communications Commission (FCC) in the United States. However, the table of standards shown below (Table 12.2) was rejected by the FCC because of pressure from the computer industry. The idea, then, was to leave the choice of what standards to use to the marketplace as long as it worked with the MPEG-2 compression scheme. The result has been that all manufacturers and broadcasters have been using the standards included in the ATSC table.

HDTV、SDTV 和 EDTV 共同构成了 18 种不同的 ATSC 图像显示格式。

Together, HDTV, SDTV, and EDTV make up 18 different ATSC picture display formats.

水平线列包含图像中的线数，而水平像素是每条线上的像素数。在“格式”列中，“i”是指扫描的图像 使用隔行扫描方法，而“p”指的是逐行扫描的图像。24 fps 也用来表示每秒 23.976 帧，而 30 fps 也用来表示每秒 29.97 帧。

The Horizontal Lines column contains the number of lines in the image, while the Horizontal Pixels is the number of pixels across each line. In the Format column, the “i” refers to images scanned using the interlace approach, while the “p” refers to progressively scanned images. 24 fps is also used to refer to 23.976 frames per second and 30 fps is also used to refer to 29.97 frames per second.

表 12.2 ATSC 图片显示格式

Table 12.2 ATSC Picture Display Formats

数字电视传输

Digital Television Transmission

数字视频需要不同于模拟的传输形式。在模拟中，视频使用 AM 图像和 FM 音频进行广播。但是数字包含一个数据流中的所有元素。由于可以压缩数字信号以减少使用与模拟频谱空间相比，多个数字数据流可以在仅包含一个模拟信号的同一空间中传输。为利用此功能，ATSC 制定了传输数字电视的新标准。

Digital video requires a different form of transmission from analog. In analog, the video was broadcast using AM for the images and FM for the audio. But digital contains all the elements in one data stream. Since digital signals can be compressed to use less spectrum space than analog, several digital data streams can be transmitted in the same space that contained just the one analog signal. To take advantage of this capability, the ATSC developed new standards for transmitting digital television.

虽然美国政府强制要求对数字电视进行更改，但并未命令所有电视广播都必须是高清的，只是要求它是数字的。由于高清 (HD) 电视不是强制性的，而且压缩数字信号所需的频谱空间比模拟信号小得多，因此广播公司可以传输高清信号和多个标准清晰度 (SD) 或增强清晰度 (ED) 信号剩余的频谱空间。这称为多播。

While the U.S. government mandated a change to digital television, it did not order that all television broadcasting must be High Definition, only that it be digital. As High Definition (HD) television is not mandatory and as compressed digital signals can require considerably less spectrum space than analog signals, broadcasters can transmit both a High Definition signal and more than one Standard Definition (SD) or Enhanced Definition (ED) signal in the remaining spectrum space. This is called multicasting.

传输数字电视信号的A/53标准称为8VSB，代表8级残余边带。残留元素是指没有任何有用价值的东西的一部分。在这种情况下，残留是指被过滤掉的不需要的那部分载波频率。它使用调制载波频率的幅度调制 (AM) 方法。采用8VSB的A/53标准可以同时传输18种不同的视频标准，并具有根据需要扩展和变化的能力。8VSB 载波调制系统对于电视传输也非常有用，因为它大大节省了带宽，是一种相对简单的调制方法，并节省了接收机设计成本。这种能力也是使多播成为可能的原因。

The A/53 standard for transmitting digital television signals is called 8VSB, which stands for 8-level vestigial sideband. A vestigial element is a part of something that has no useful value. Vestigial in this case refers to that part of the carrier frequency that is filtered off as unnecessary. It uses the amplitude modulation (AM) method of modulating a carrier frequency. The A/53 standard using 8VSB can transport 18 different video standards simultaneously and has the capability to expand and change as needed. The 8VSB system of carrier modulation is also very useful for television transmission in that it greatly conserves bandwidth, is a relatively simple method of modulation, and saves cost in receiver design. This capability is also what makes multicasting possible.

为了传输，将 MPEG-2 节目数据、音频数据、辅助或附加数据（例如关于数据流中包含的内容的说明、隐藏式字幕和同步信息）组合或多路复用到数据流中。该数据流是为传输而发送的。

For transmission, the MPEG-2 program data, the audio data, the ancillary or additional data such as instructions about what is contained in the data stream, closed captioning, and synchronizing information are combined or multiplexed into the data stream. This data stream is what is sent for transmission.

数字有线虽然遵循采用的ATSC标准，但一般不使用8VSB进行信号调制。代替电缆运营商使用一种更复杂的调制形式，称为正交幅度调制(QAM)，它能够提供 64 或 256 级，而不是 8VSB 的 8 级。

Digital cable, while adhering to the adopted ATSC standards, generally does not use 8VSB for signal modulation. Instead cable operators use a more complex form of modulation called quadrature amplitude modulation (QAM) that is capable of 64 or 256 levels rather than the 8 levels of 8VSB.

卫星广播使用另一种调制形式，称为正交相移键控(QPSK)。同样，用于卫星广播的标准遵循 ATSC 表，但卫星广播公司使用 QPSK 来调制载波信号。

Satellite broadcasting uses another form of modulation called quadrature phase-shift keying (QPSK). Again, the standards used for satellite broadcasting adhere to the ATSC table but satellite broadcasters use QPSK for modulating the carrier signal.

向前进

Moving Forward

视频技术将继续发展。“电视”观众将希望在越来越多的媒体资源和传送平台（当然包括互联网）上以各种方式观看他们的节目。未来必须开发包含这些元素的新 DTV 系统，以跟上行业技术发展和消费者期望的步伐。ATSC 已经在为适应未来创新的 3.0 系统制定计划。展望未来，这个新系统必须解决新兴技术的一些关键概念，使其具有可扩展性、可互操作性和适应性。

Video technology will continue to evolve. And “television” viewers will want to watch their programs in a variety of ways on a growing range of media sources and delivery platforms, including, of course, the Internet. Creating a new DTV system that incorporates these elements must be developed in the future to keep pace with the industry’s technological growth and that of the consumers’ expectations. The ATSC is already making plans for a 3.0 system that will adapt to future innovations. Moving forward, this new system must address some of the key concepts of the emerging technology, by making it scalable, interoperable, and adaptable.

设定高清标准

Setting High Definition Standards

1990 年代初期，另一个组织国际电信联盟 (ITU) 开始参与推荐电视标准。国际电联是联合国专门机构，负责弥合世界各地在信息和通信技术（简称 ICT）方面的差距。国际电联有不同的部门，解决电视行业推荐用途的部门是无线电通信部门或 ITU-R。专注于视频的 ITU-R 研究组是广播服务（电视）学习小组。该小组针对高清标准提出的建议是文件 ITU-R Recommendation BT.709.5（用于制作和国际节目交换的 HDTV 标准的参数值）。

In the early 1990s, another organization, the International Telecommunication Union (ITU), became involved in recommending television standards. The ITU is the United Nations specialized agency for bridging gaps throughout the world in Information and Communication Technologies (referred to as ICTs). There are different sectors of the ITU, and the sector that addresses recommended uses in the television industry is the Radiocommunication sector, or ITU-R. The ITU-R study group that focuses on video is the Broadcasting Service (Television) study group. And the recommendation that group laid out for high definition standards is the document, ITU-R Recommendation BT.709.5 (parameter values for the HDTV Standards for production and international program exchange).

为了创建采用标准的统一方法，三个世界领先的国际标准组织于 2001 年联合成立了世界标准合作组织 (WSC)。该组织由 ISO、ITU 和国际电工委员会 (IED) 建立。WSC 向前发展的目的是加强和推进 ISO、IEC 和 ITU 的基于自愿共识的国际标准体系。

To create a unified approach to adopting standards, three of the world’s leading international standards organization came together in 2001 to form the World Standards Cooperation (WSC). This organi zation was established by ISO, ITU, and the International Electrotechnical Commission (IED). The purpose of the WSC moving forward is to strengthen and advance the voluntary consensus-based international standards systems of ISO, IEC, and ITU.

今天，有几种不同的高清标准，每一种都有自己独特的图像标准组合，包括帧速率、像素数、线数和扫描模式。

Today, there are several different high def standards, each with its own unique combination of image criteria, including frame rate, pixel count, line count, and scanning mode.

宽屏纵横比

Widescreen Aspect Ratio

CDTV 和 SDTV 标准使用纵横比为 4 × 3 的图像尺寸。4 × 3 图像的宽度为四个单位，高度为三个单位。虽然它是矩形的，但它比目前在电影院看到的宽屏图像更接近正方形。人眼从直接视野之外的区域感知大量运动和深度信息。这个区域被称为周边视觉。有一个 更宽的视频图像区域利用了这一特性，提高了观看者的真实感。

CDTV and SDTV standards use an image size with an aspect ratio of 4 × 3. A 4 × 3 image is four units wide by three units high. While rectangular in shape, it is much closer to a square than the wide-screen image currently seen in cinemas. The human eye perceives a great deal of motion and depth information from the area outside of direct view. This area is known as peripheral vision. Having a wider video image area takes advantage of this characteristic and improves the sense of reality for the viewer.

图 13.1 4 × 3 和 16 × 9 纵横比

Figure 13.1 4 × 3 and 16 × 9 Aspect Ratios

随着 HDTV 的发展，这一事实被考虑在内，所有 HDTV 标准都被扩大到 16 × 9 的宽高比，或九个单位高乘以十六个单位宽的图像（图 13.1 ）。由于 HDTV 标准都有 16 × 9 的比例，因此通常称为标准的宽高比。本地标准是设计设备的基本标准。它可能能够处理其他标准，但它的初衷是称为本机标准。

As HDTV was developed, this fact was taken into consideration and all HDTV standards were widened to a 16 × 9 aspect ratio, or an image that is nine units high by sixteen units wide (Figure 13.1). Since the HDTV standards all have a 16 × 9 ratio, it is often referred to as the aspect ratio for the standard. A native standard is the basic standard for which the piece of equipment was designed. It may be capable of handling other standards, but its original intent is called the native standard.

宽屏视频可以不同方式在 4 × 3 显示器上播放。要查看整个宽屏图像，必须缩小图像尺寸，使图像宽度适合 4 × 3 显示器。这会在宽屏图像上方和下方创建黑色，这种布局通常称为信箱。要利用完整的 4 × 3 图像区域，可以裁剪宽屏图像的两侧以仅显示中间部分或 4 × 3 区域。此外，可以在传输过程中应用平移或水平移动图像的过程，以显示宽屏图像的特定部分。这个过程通常称为平移和扫描（图 13.2）。

Widescreen video can be played back on a 4 × 3 monitor in different ways. To see the entire widescreen image, the image must be reduced in size so the width of the image fits on the 4 × 3 monitor. This creates black above and below the widescreen image, a layout often referred to as letterbox. To make use of the full 4 × 3 image area, the sides of the widescreen image can be cropped to show just the middle portion, or 4 × 3 area. Also, a process of panning, or moving horizontally across an image, can be applied during transfer to reveal a particular portion of the widescreen image. This process is often called pan and scan (Figure 13.2).

图 13.2 16 × 9 转换为 4 × 3 纵横比

Figure 13.2 16 × 9 Converted 4 × 3 Aspect Ratios

4 × 3 的素材也可以在宽屏显示器上显示。内容创建者可以选择如何处理纵横比转换。如果将较小图像的顶部和底部放大到接触 16 × 9 光栅的顶部和底部，则图像的左侧和右侧将保留一个空白区域。如果这是黑色的，则称为邮筒展示。当在侧面添加图形元素时，术语翼有时用于表示左右黑色区域。最后，可以进一步放大图像，以匹配两个纵横比的左右边缘。这将丢弃原始 4 × 3 帧顶部和底部的一部分。它还会导致非常明显的图像柔化。

4 × 3 material can also be displayed on a widescreen monitor. The content creator can choose how to deal with the aspect ratio conversion. If the top and bottom of the smaller image is enlarged to touch the top and bottom of the 16 × 9 raster, an empty area will be remain on the left and right of the image. If this is left black it is referred to as pillar box presentation. When graphic elements are added on the sides, the term wings is sometimes used for the left and right black areas. Finally the image can be enlarged further, matching the left and right edges of both aspect ratios. This will discard a portion of the top and bottom of the original 4 × 3 frame. It also leads to quite visible softening of the image.

高清图像分辨率

HD Image Resolution

在 16 × 9 的宽高比下，图像区域更大，因此有更多空间容纳额外的像素。不同的高清标准具有构成该标准图像区域的不同像素和行数。构成图像的像素数量越多，图像的分辨率就越高。

With the 16 × 9 aspect ratio, there is a larger image area and therefore more room for additional pixels. Different high def standards have different pixel and line counts that make up that standard’s image area. The greater the number of pixels that make up the image, the greater the image resolution.

例如，一种高清格式的图像分辨率为 1920 × 1080。在这种格式中，一行有 1920 个像素，一帧图像有 1080 行。1920 像素数是水平分辨率，1080 行数是垂直分辨率。另一个高清标准是 1280 × 720，即每行 1280 像素 x 720 行。组合的像素和行数构成了高清图像的空间密度分辨率。

For example, one high def format has an image resolution of 1920 × 1080. In this format, there are 1920 pixels across one line and 1080 lines in one frame of the image. The 1920 pixel count is the horizontal resolution, and the 1080 line count is the vertical resolution. Another high def standard is 1280 × 720, which is 1280 pixels per line by 720 lines. The combined pixel and line count make up the spatial density resolution of the high def image.

超高清

Ultra High Definition

就像静止图像相机的百万像素数量迅速增加一样，视频系统继续开发更高分辨率的成像。随着技术发展出更快的处理速度、更好的压缩算法和更精确的制造技术，更高分辨率的设备成为可能。分辨率高于标准 HD 的图像称为 UHD，即超高清。

Much like the rapid increase in megapixel count for still image cameras, video systems continue to develop higher resolution imaging. As technology develops faster processing, better compression algorithms and more precise manufacturing techniques, higher resolution equipment is possible. Images that have a higher resolution than the standard HD are referred to as UHD, or Ultra High Definition.

8K

8K

4K好，8K会更好吗？日本广播公司 NHK 正在开发下一代高分辨率技术。这种格式称为 8K，在其 4320 行中的每一行上都有 7680 个像素。

If 4K is good, will 8K be better? The broadcaster, NHK, in Japan is developing the next generation of High Resolution technology. Called 8K, this format has 7680 pixels on each of its 4320 lines.

这几乎是 4K 的像素和线数的两倍。此外，这种格式正在考虑高达每秒 120 帧的帧速率。为了增强音频体验，该格式指定了 22.2 声道的环绕声。近年来，NHK 多次展示了这种格式的原型，并希望从 2020 年东京奥运会开始播放这种格式。除了 NHK，索尼和 Red Digital Cinema Camera Company 也在努力在未来几年将 8K 传感器引入他们的摄像机。

This is almost twice as many pixels and lines as 4K. In addition, frame rates up to 120 fames per second are being considered for this format. To enhance the audio experience, the format specifies surround sound with 22.2 channels. NHK has shown the format in prototype form numerous times in recent years, and hopes to broadcast the format starting with the 2020 Olympic Games in Tokyo. In addition to NHK, Sony and Red Digital Cinema Camera Company are working to bring 8K sensors into their cameras in the coming years.

使用 8K 的优势之一是其超高分辨率允许在后期制作过程中有更多选择。如上所述，使用 4K 拍摄体育回放时，使用 8K 可以拍摄广角图像，可能是远处有潜在危险的动物，然后进行数字缩放、裁剪或平移并扫描图像以仅使用所需的部分。放大的部分仍将与当前行业标准高清电视的较小分辨率相匹配。此外，与 4K 相机相比，8K 相机传感器可生成更清晰的图像和更丰富的色彩。但是 8K 图像可以降采样到 4K，以较低的分辨率创建更好的图像。

One advantage of working with 8K is that its super-high resolution allows for more options during the post production process. As mentioned above with 4K shooting a sports replay, with 8K you can shoot an image in wide shot, perhaps a potentially dangerous animal far away, and then digitally zoom and crop or pan and scan the image to use just the desired portion. The zoomed-in portion would still match the smaller resolution of the current industry standard HD televisions. Also, 8K camera sensors create sharper pictures and richer colors than a 4K camera. But the 8K image can be downsampled to 4K, creating a better picture with a lower resolution.

调制传递函数 (MTF)

Modulation Transfer Function (MTF)

在讨论分辨率时，很容易忘记数字图像传感器捕捉的是模拟世界。虽然图像捕捉技术以计算机系统的快速发展，但镜头和棱镜系统的光学技术往往难以跟上。在光学上，图像清晰度和对比度是相关的，并通过称为调制传递函数或 MTF 的东西来衡量。测量方法是使用包含成对黑白线条的成像测试图（图 13.3）。

When discussing resolution, it’s easy to forget that the digital image sensors are capturing the analog world. While the technology of image capture advances at the rapid rate of computer systems, often the optical technology of the lens and prisms systems struggle to keep up. Optically, image sharpness and contrast are related and measured by something called the Modulation Transfer Function, or MTF. The way this is measured is by using imaging test charts that contain pairs of black and white lines (Figure 13.3).

图 13.3 USAF 1951 成像测试图

Figure 13.3 USAF 1951 Imaging Test Chart

注意此图表由美国空军于 1951 年开发，这就是为什么您有时会在图表本身上看到该信息的原因。

NOTE This chart was developed by the U.S. Air Force in 1951, which is why you will sometimes see that information on the chart itself.

随着线条变得更小、靠得更近，它们变得更难复制。线条的边缘变得模糊在一起，混合产生柔和的灰色图像。较低的点线条合并为灰色的对比度表示光学系统可以传输到图像的锐度极限。

As the lines get smaller and closer together they become more difficult to reproduce. The edges of the lines become blurred together, mixing to produce soft gray images. The point where the lower contrast of the lines merge to gray represents the limit of sharpness the optical system can transfer to the image.

尽管手机或便宜的相机可以很好地进行 4K 录制，但廉价的量产镜头将无法创建足够高的分辨率来复制图表中清晰的线条划分，如图 13.3所示。

Although a cell phone or inexpensive camera may well make a 4K recording, the inexpensive mass-produced lens will not be able to create a high enough resolution to replicate clear line divisions in charts such as in Figure 13.3.

渐进式分段帧

Progressively Segmented Frames

HDTV 标准可以使用两种扫描模式中的任何一种，即隔行扫描或逐行扫描。当高清标准使用隔行扫描模式时，首先传输奇场，然后传输偶场，就像在 CDTV 或 SDTV 中一样。在逐行扫描中，整个图像被扫描为一个完整的帧。该数据随后可作为完整帧传输并作为完整帧接收。如果没有足够的带宽来传输完整的帧，则可以将数据分段并分两部分传输。

HDTV standards can use either of the two scanning modes, interlace or progressive. When a high def standard uses an interlace mode, the odd fields are transmitted first, followed by the even fields, just as they are in CDTV or SDTV. In progressive scanning, the entire image is scanned as one complete frame. This data may then be transmitted as a complete frame and received as a complete frame. If there is insufficient bandwidth to transmit the complete frame, the data may be segmented and transmitted in two parts.

由于逐行扫描图像是完整的视频帧，因此它们需要比可用带宽更多的带宽来传输。为了使用较窄的带宽在隔行扫描环境中传输这些图像，开发了一种分段逐行扫描帧的过程。

Because progressively scanned images are complete frames of video, they require more bandwidth to transmit than may be available. To transmit these images within an interlace environment using narrower bandwidths, a process of segmenting progressively scanned frames was developed.

为此，像隔行扫描一样，每隔一行扫描一次，将图像分成两个场。不同的是，在隔行扫描过程中，两个场来自不同的时间点。当逐行扫描图像被分割时，这两个字段来自同一时间实例。当单独的场重新组合时，结果是一个完整的逐行扫描帧（图 13.4）。

To do this, the image is divided into two fields by scanning every other line as in interlace scanning. The difference is that, in the interlace scanning process, the two fields are from different instances in time. When a progressively scanned image is segmented, the two fields are from the same instance in time. When the separate fields are recombined, the result is a complete progressively scanned frame (Figure 13.4).

图 13.4 (A)隔行扫描和(B)逐行分段帧

Figure 13.4(A) Interlace Scan and (B) Progressive Segmented Frame

此过程满足了在不影响图像质量的情况下分割数据的需要。渐进式扫描然后作为分段帧传输的图像称为 PsF，即渐进式分段帧。

This process accommodates the need to segment the data without compromising the quality of the image. Images that are progressively scanned and then transmitted as segmented frames are referred to as PsF, for Progressively Segmented Frames.

帧率

Frame Rate

在 HDTV 标准集中，有许多帧速率。帧速率是定义特定 HDTV 标准的一组标准的一部分。由于现有物理环境中的特定要求，定义了每组标准。例如，北美电气系统使用 60 周期交流电电流，而欧洲电气系统使用 50 周期交流电。

Within the HDTV set of standards, there are numerous frame rates. The frame rates are part of a set of criteria that defines a particular HDTV standard. Each set of criteria was defined because of specific requirements within an existing physical environment. For example, North American electrical systems use 60-cycle alternating current, while European electrical systems use 50-cycle alternating current.

此外，影像创作的主要形式之一是电影。影片在北美以每秒 24 帧的速度运行，在欧洲以每秒 25 帧的速度运行。为了尽量减少将电影融入 HDTV 的难度，制定了一套标准来适应电影帧率。根据新标准与现有系统接口的难易程度，根据一组特定标准创建了不同的 HDTV 标准。因此，许多 HDTV 标准中的两个包括 24 fps 和 25 fps。

In addition, one of the major forms of image creation has been film. Film runs at 24 fps in North America and 25 fps in Europe. To minimize the difficulty in incorporating film into HDTV, a set of criteria was developed to accommodate the film frame rate. A different HDTV standard was created with a specific set of criteria based on the ease with which the new standard would interface with an existing system. Therefore, two of the many HDTV standards include 24 fps and 25 fps.

胶片到磁带转换

Film-to-Tape Conversion

将电影转换为 HDTV 或将 HDTV 转换为电影的情况有很多。电影经常被用作档案媒体，因为电影标准几代人都没有改变。当使用电影作为原始媒体但交付要求是视频时，电影必须经过转换过程。将胶片转换为电子形式通常称为电视电影，也可以指转换过程中使用的机器。在 PAL 系统中，现有的视频帧速率与 25 fps 的电影速率相匹配，转换过程只是从一种媒体转换为另一种媒体的问题。然而，在 NTSC 系统中，30 fps 的视频帧速率与 24 fps 的电影速率不匹配，必须进行不同的转换过程。

There are many situations when film is transferred to HDTV, or HDTV to film. Film is often used as an archival medium because the film standard has not changed in generations. When film is used as the originating medium but the delivery requirement is video, film must go through a conversion process. Converting film to an electronic form is often referred to as telecine, which can also refer to the machine used in the conversion process. In PAL systems, the existing video frame rate matches the 25 fps film rate, and the conversion process is simply a matter of converting from one medium to the other. However, in the NTSC system, where the video frame rate of 30 fps does not match the film rate of 24 fps, a different conversion process must take place.

转换不同的帧率源

Converting Different Frame Rate Sources

无论是从电影到视频还是从视频到视频的转换需求，HDTV 24 fps 标准都使视频和电影更加兼容，尤其是在电影盛行的美国以每秒 24 帧的速度拍摄。但是，要从每秒生成 24 个图像的源在视频中创建每秒 30 个图像，需要添加额外的视频字段。这是通过从 24 fps 源复制图像来完成的。添加额外字段以创建额外帧的过程称为 2:3下拉系统，有时也称为 3:2下拉系统。

Whether the need for conversion is from film to video or video to video, the HDTV 24 fps standard makes video and film more compatible with each other, especially in the United States where film is shot at 24 fps. However, to create 30 images per second in video from a source producing 24 images per second, additional video fields are added. This is done by duplicating images from the 24 fps source. The process of adding additional fields to create additional frames is known as a 2:3 pulldown system or sometimes as a 3:2 pulldown system.

当用于图像捕获的 24 fps 逐行扫描视频必须转换为 30 fps 以进行编辑或传输时，使用 2:3 或 3:2 下拉过程。将 24 fps 电影转换为 30 fps 视频时也会使用它。将 24 fps 电影或视频转换为 30 fps 视频系统时，必须决定使用哪个序列（2:3 或 3:2），然后保持该序列。

The 2:3 or 3:2 pulldown process is used when 24 fps progressive scan video, used in image capture, must be converted to 30 fps for either editing or transmission. It is also used when transferring 24 fps film to 30 fps video. When transferring 24 fps film or video into a 30 fps video system, it is essential to decide which sequence will be used—2:3 or 3:2—and then maintain that sequence.

使用 2:3 和 3:2 下拉序列

Using 2:3 and 3:2 Pulldown Sequences

当以 2:3 序列每秒传输 24 帧时，系统会将四帧从原始源映射到每五帧或十场到传输源。传输的第一个帧称为 A 帧。它被转移或下拉到两个视频场。第二帧称为 B 帧，并被传送到接下来的三个连续视频场。第三个电影帧，C 帧，被转移到接下来的两个连续视频帧。第四帧，即 D 帧，被转移到接下来的三个连续视频帧（图 13.5）。

When transferring 24 frames per second in a 2:3 sequence, the system will map four frames from the original source to every five frames, or ten fields, to the transfer source. The first frame that is transferred is referred to as the A frame. It is transferred, or pulled down, to two video fields. The second frame is referred to as the B frame and is transferred to the next three consecutive video fields. The third film frame, the C frame, is transferred to the next two consecutive video frames. And the fourth frame, the D frame, is transferred to the next three consecutive video frames (Figure 13.5).

由此产生的传输过程为每四个原始 24 fps 源帧生成五个视频帧。视频帧 1 和视频帧 2 分别来自两个独立的电影帧 A 和 B。但是，视频帧 3 是电影帧 B 的一个场和电影帧 C 的一个场的合成。视频帧 4 也是一个由胶片帧 C 的一个场和胶片的一个场组成的复合材料 帧 D。视频帧 5 由两个场组成，均来自电影帧 D。

The resulting transfer process yields five video frames for every four original 24 fps source frames. Video frame 1 and video frame 2 are each derived from two separate film frames, A and B. Video frame 3, however, is a composite of one field from film frame B and one field from film frame C. Video frame 4 is also a composite composed of one field from film frame C and one field from film frame D. Video frame 5 is composed of two fields, both from film frame D.

图 13.5 2:3 下拉序列

Figure 13.5 2:3 Pulldown Sequence

当扫描使用此过程传输的视频图像时，包含两个不同帧的视频帧将显示为双图像。然而，当这些帧在运动中被观察时，双重图像是不可辨别的。使用此下拉过程编辑从胶片传输的视频时，必须保持帧的顺序。如果视频帧的顺序被打断，例如连续编辑两个组合帧，则在运动显示时将可辨别由此产生的图像冲突。

When scanning through video images that have been transferred using this process, the video frames that contain two different frames will appear as a double image. When these frames are viewed in motion, however, the double image is not discernible. When editing video that has been transferred from film using this pulldown process, the sequence of frames must be maintained. If the sequence of video frames is broken, for example by editing two combination frames consecutively, the resulting conflict of images will be discernible when displayed in motion.

当下拉序列更改为 3:2 时，生成的帧会产生不同的结果。五个视频帧将是 AA AB BC CC DD（图 13.6）。这里第二和第三帧是合成的，而不是第三和第四帧。在 在 3:2 序列中，有一个干净的帧，然后是两个复合帧，然后是两个干净的帧。因此，在将 24 fps 转换为 30 fps 时，必须始终如一地应用这些过程之一，以便保持干净帧和合成帧的顺序。

When the pulldown sequence is changed to 3:2, the resulting frames yield a different result. The five video frames would be AA AB BC CC DD (Figure 13.6). Here the second and third frames are composite, rather than the third and fourth. In the 3:2 sequence there is one clean frame followed by two composite frames followed by two clean frames. Therefore, when converting 24 fps to 30 fps, it is essential that one of these processes is applied consistently so the order of clean and composite frames will be maintained.

图 13.6 3:2 下拉序列

Figure 13.6 3:2 Pulldown Sequence

保持下拉序列的一致性

Maintaining Consistency in Pulldown Sequences

正如下拉序列必须保持不变一样，传输过程也应如此。一旦开始传输场景或部分，就必须不停地完成传输。如果传输停止然后在单个场景或序列中重新启动，系统将再次假定第一帧是 A 帧并从那里开始序列。稍后，当尝试在视频中一起编辑此序列时，帧序列很可能已被破坏，并且编辑后的版本将包含来自不兼容帧的重叠图像。结果可能是图像中的断断续续或跳跃。

Just as the pulldown sequence must remain constant, so should the transfer process. Once the transfer of a scene or section has begun, it is essential the transfer be completed without stopping. If the transfer is stopped and then restarted in a single scene or sequence, the system will assume the first frame again is an A frame and begin the sequence from there. Later, when attempting to edit this sequence together in video, it is very possible that the frame sequence will have been broken and the edited version will contain overlapped images from incompatible frames. The result could be a stutter or jump in the images.

在电影或视频传输过程中，当镜头被数字化到视频系统中时，可以创建一个计算机文件，该文件将指示每个部分的相关复合帧的位置。还可以通过一次滚动视频一个字段来查看和识别添加的字段。使用正确编译的计算机文件，视频系统可以提取并重新组合重叠场，从视频传输中创建的 30 fps 2:3 或 3:2 下拉序列创建干净的 24 fps 序列。该过程将丢弃用于从原始 24 fps 材料创建 30 fps 视频的冗余字段。这个过程被称为反向电视电影。

During the film or video transfer process, as the footage is digitized into the video system, a computer file can be created that will indicate where the associated composite frames are for each section. The added fields can also be seen and identified by scrolling through the video a field at a time. With a correctly compiled computer file, it is possible for a video system to extract and recombine the overlapping fields to create a clean 24 fps sequence from the 30 fps 2:3 or 3:2 pulldown sequence created in the video transfer. The process will discard the redundant fields used to create the 30 fps video from the original 24 fps material. This process is referred to as inverse telecine.

转换高清信号

Converting an HD Signal

HDTV 和 SDTV 之间的主要区别之一是构成 HDTV 信号的信息量有所增加。由于每行的像素数、每帧的行数和每秒的帧数，HDTV 具有更高的空间和时间分辨率。虽然图像尺寸更大，分辨率更高，但记录、存储和传输过程仍然相似。由于这些相似性，HDTV 信号可能会转换为其他标准。

One of the primary differences between HDTV and SDTV is the increase in the amount of information that makes up the HDTV signal. Because of the number of pixels per line, lines per frame, and frames per second, HDTV has a greater spatial and temporal resolution. While the size of the image is larger and the resolution is greater, the recording, storage, and transmission processes remain similar. Because of these similarities, HDTV signals may be converted to other standards.

将 HDTV 转换为 SDTV 或 CDTV 称为下转换。在下转换过程中，行数和每行像素数会减少以符合目标标准。例如，1920 × 1080 的 HDTV 图像可以缩小为 720 × 480 的 SDTV 图像。减少是通过在下转换过程中删除一些线和像素来实现的。这样做的结果是图像分辨率降低，尽管纵横比可能保持不变。但是，在某些情况下，当 16 × 9 图像缩小为 4 × 3 时，4 × 3 图像可能看起来比原始图像具有更多细节。

Converting HDTV to SDTV or CDTV is referred to as down converting. In the downconversion process, the number of lines and the number of pixels per line are reduced to fit the targeted standard. For example, a HDTV image that is 1920 × 1080 could be reduced to a 720 × 480 SDTV image. The reduction is achieved by deleting some lines and pixels in the downconversion process. The consequence of this is a reduction in image resolution, though the aspect ratio may remain the same. However, in some situations when a 16 × 9 image is reduced to 4 × 3, the 4 × 3 image may appear as though it had greater detail than the original.

图 13.7 HD VCR 上的下变频器

Figure 13.7 Down Converter on HD VCR

当需要在 SDTV 或 CDTV 环境中使用 HDTV 原始图像时，将使用下转换。例如，一个节目可以用 HDTV 拍摄，但可以用 SDTV 甚至 CDTV 传输或播放。此外，如果编辑过程配置了 SDTV 或 CDTV 设备，从 HDTV 下转换允许在现有的后期制作环境中进行编辑。一些 HD VCR 甚至可以在内部对信号进行下变频（图 13.7）。

Downconversion is used when an HDTV native image needs to be used in an SDTV or CDTV environment. For example, a program can be shot in HDTV, but transmitted or broadcast in SDTV or even CDTV. Also, if the editing process is configured with SDTV or CDTV equipment, a downconversion from HDTV allows the editing to occur within the existing post production environment. Some HD VCRs are even equipped to downconvert a signal internally (Figure 13.7).

CDTV 或 SDTV 也可以通过称为上转换的过程转换为 HDTV 标准。上转换过程增加了行数和每行像素数以符合目标标准。在某些情况下，这涉及复制信息以填充额外的空间分辨率。这不会增加图像的细节，也不会增加表观分辨率。它只会增加像素和行数。

CDTV or SDTV can also be converted to an HDTV standard through a process called upconverting. The upconversion process increases the number of lines and the number of pixels per line to fit the targeted standard. This involves, in some instances, duplication of information to fill in the additional spatial resolution. This does not increase the detail in the image nor the apparent resolution. It merely increases the pixel and line count.

在拍摄 CDTV 或 SDTV 图像并将其放大以适合 HDTV 空间时使用上转换。例如，起源于 CDTV 的旧电视节目可能会被上转换为 HDTV 或 SDTV 以供当前广播。某些设备在机器内部包含一个下变频/上变频电路。

Upconversion is used when taking a CDTV or SDTV image and enlarging it to fit in an HDTV space. For example, an older television program that originated in CDTV may be upconverted to HDTV or SDTV for current broadcast. Some equipment contains a downconversion/upconversion circuit within the machine itself.

在其他情况下，转换过程是通过外接或独立设备完成的。

In other cases, the conversion process is accomplished through an outboard or stand-alone device.

高清电视应用

HDTV Applications

由于不同的 HDTV 扫描类型和帧速率，HDTV 图像在每个标准下看起来可能不同。较快的扫描速率或时间分辨率（典型的隔行扫描）可提供更频繁的图像信息，因为它为每个帧扫描图像两次，一次用于奇数行，一次用于偶数行。扫描是在不同的时刻创建的。此过程比逐行扫描更频繁地刷新图像。因此，隔行扫描通常用于包含大量运动细节的图像。例如，经常使用 60 场隔行扫描 (60i) HDTV 拍摄足球比赛。更频繁地扫描图像场会在给定的时间内产生更多数量的图像，从而在场与场之间以及帧与帧之间创建更平滑的过渡。

Because of the different HDTV scanning types and frame rates, HDTV images may look different with each standard. A faster scan rate, or temporal resolution, typical of interlace scanning, gives more frequent image information because it scans an image twice for each frame, once for the odd lines and again for the even lines. The scans are created in different moments in time. This process refreshes the image more frequently than progressive scanning. Therefore, interlace scanning is often used for images that contain a great detail of motion with a lot of action. For example, football games are often shot using 60-field interlace (60i) HDTV. The more frequent scanning of the image fields produces a greater number of images in a given amount of time, creating a smoother transition from field to field and frame to frame.

以 24p 或 24 fps 逐行扫描拍摄的 HDTV 图像会提供较低的扫描频率或较慢的时间分辨率。以 24p 拍摄意味着扫描全帧需要更长的时间，因为必须扫描连续的行。24p 的帧速率营造出更柔和的电影效果。在 24p 中，快速运动是不可取的，因为较慢的时间分辨率无法捕获足够的运动细节以清晰地跟踪动作。

An HDTV image shot in 24p, or 24 fps progressive scanning, gives a less frequent scanning rate or slower temporal resolution. Shooting in 24p means it takes longer to scan a full frame because successive lines must be scanned. A 24p frame rate creates a softer, film-like look. In 24p, rapid motion is not advisable because the slower temporal resolution cannot capture enough motion detail to track the action clearly.

24p 被开发为标准的原因之一是在时间和空间分辨率方面与 35mm 电影胶片相匹配。某些源自 SD 视频的电视节目被转换为 HDTV 以供存档，有时还用于广播目的。然而，在 HDTV 出现之后创建的节目，但在当时 HDTV 标准仍在制定中定义，转向电影制作目的。这使得节目既可以在电影这种既定媒体中存档，又可以在以后转换为任何视频标准。

One of the reasons 24p was developed as a standard was to match 35mm motion picture film, both in terms of temporal and spatial resolution. Certain television programs that originated in SD video are converted to HDTV for archival and sometimes broadcast purposes. However, shows that were created after the advent of HDTV, but during the time HDTV standards were still being defined, turned to film for production purposes. This allowed the shows to be both archived in film, an established medium, and converted to any video standard at a later date.

非图片数据

Non-Picture Data

数字视频使用数据流来承载图像信息，但其中也夹杂着非图像数据。这些非图片数据中的一些包含同步和颜色信息，还有一些包含有关图片数据流本身的信息。该数字数据流还包含有关正在使用哪些标准的信息。

Digital video uses a data stream to carry picture information, but there is also non-picture data mixed in with it. Some of this non-picture data contains sync and color information, and some of it contains information about the picture data stream itself. This digital data stream also contains information about which standards are being used.

垂直辅助数据 (VANC)

Vertical Ancillary Data (VANC)

在模拟视频信号中，场与场之间的垂直消隐间隔用于承载同步信息，最终包括测试信号、时间码和隐藏式字幕数据。在数字视频中，该数据现已合并到数据流中，并包含在 VANC 或垂直辅助数据的标题下。VANC 被创建并通过数据编码器编码到数据流中，该数据编码器创建并还可以检索信息。要编码的数据由操作员通过编码器内置的一系列菜单进行编程。

In analog video signals, the vertical blanking interval between fields was used to carry synchronizing information and eventually included test signals, timecode and closed captioning data. In digital video this data has now been incorporated into the data stream and is included under the heading of VANC, or vertical ancillary data. VANC is created and encoded into the data stream through a data encoder that creates and can also retrieve the information. The data to be encoded is programmed in by the operator through a series of menus built into the encoder.

水平辅助数据 (HANC)

Horizontal Ancillary Data (HANC)

除了 VANC 之外，还有 HANC 或水平辅助数据。这类似于与逐行同步和颜色同步相关的水平消隐间隔中携带的数据。

In addition to VANC, there is also HANC or horizontal ancillary data. This is analogous to the data carried in the horizontal blanking interval that relates to line-by-line synchronization and color synchronization.

无损压缩

Lossless Compression

在无损压缩中，可以从原始图像中包含的压缩数据完美地重建原始数据。压缩文档是一种无损压缩形式，因为恢复的文档必须与原始文档完全相同。它不可能是一个近似值。在视觉世界中， 无损压缩适用于包含大量重复信息的图像，例如包含大面积一种颜色的图像，也许是蓝天。计算机生成的图像或不包含太多细节的平面彩色区域（例如，卡通、图形和 3D 动画）也适用于无损压缩。

In lossless compression, the original data can be perfectly reconstructed from the compressed data that was contained in the original image. Compressing a document is a form of lossless compression in that the restored document must be exactly the same as the original. It cannot be an approximation. In the visual world, lossless compression lends itself to images that contain large quantities of repeated information, such as an image that contains a large area of one color, perhaps a blue sky. Computer-generated images or flat colored areas that do not contain much detail—e.g., cartoons, graphics, and 3D animation—also lend themselves to lossless compression.

图 14.1 无损压缩与有损压缩

Figure 14.1 Lossless vs Lossy Compression

图形和计算机生成图像 (CGI) 中常用的一种无损压缩是游程编码。这些图像往往有很大一部分使用相同的颜色或重复的图案。数字图像中的每个像素都由三种颜色组成——红色、绿色和蓝色——并且每个像素对于每种颜色都有一个特定的值。因此，它需要三个字节的信息，一个字节代表一种颜色，来表示一个像素。

One type of lossless compression commonly used in graphics and computer-generated images (CGI) is run-length encoding. These images tend to have large portions using the same colors or repeated patterns. Every pixel in a digital image is composed of the three component colors—red, green, and blue—and every pixel has a specific value for each color. Therefore, it takes three bytes of information, one byte for each color, to represent a pixel.

运行长度编码，而不是存储每个单独像素的 RGB 值，将每条扫描线分组为具有相同像素值的部分或运行长度（图 14.2 ）。例如，一行视频的一部分可能由一行 25 个黑色像素组成。本节 游程编码为 25、0、0、0。这表示 25 个像素，每个像素由 R = 0、G = 0 和 B = 0 组成，即黑色。原始图像需要 75 字节（25 像素 × 3 字节）来保存此数据。当使用游程编码压缩时，相同的数据可以包含在四个字节中。

Run-length encoding, rather than store the RGB value for each individual pixel, groups each scan line into sections, or run-lengths, of identical pixel values (Figure 14.2). For example, one section of a line of video might consist of a row of 25 black pixels. This section would be run-length encoded as 25, 0, 0, 0. This translates as 25 pixels, each composed of R = 0, G = 0, and B = 0, or black. The original image would have required 75 bytes (25 pixels × 3 bytes) to hold this data. When compressed using run-length encoding, the same data can be contained in four bytes.

图 14.2 游程编码

Figure 14.2 Run-length Encoding

有损压缩

Lossy Compression

相机生成的视频图像通常不适合无损压缩技术。图像中很少有足够长的相同像素值运行长度来最大化这些技术的效率。用于活动视频的压缩通常属于有损类别。使用有损压缩，恢复的图像将是原始图像的近似值。复制或解压缩有损图像时，并非所有在压缩过程中遗漏的数据都将完全恢复原样。

Video images generated by a camera are generally not suited for lossless compression techniques. Rarely are there long enough run lengths of the same pixel value in an image to maximize the efficiency of these techniques. Compression used for active video is usually in the lossy category. With lossy compression, the restored image will be an approximation of the original. When a lossy image is reproduced or uncompressed, not all the data left out during compression will be restored exactly as it was.

为了最大限度地减少数据的可见损失，有损压缩技术通常会压缩包含人眼不太敏感的图像部分或包含不太重要的图像数据的数据。人眼对光线水平或亮度的变化比对颜色（色调和饱和度）的变化更敏感。在色域内，人眼对黄绿蓝范围更为敏感。人眼对运动中的物体也比对静止物体更敏感。

To minimize the visible loss of data, lossy compression techniques generally compress the data that comprise those parts of the image the human eye is less sensitive to, or that contain less critical image data. The human eye is more sensitive to changes in light levels or luminance than it is to changes in color, both hue and saturation. Within the color gamut, the human eye is more sensitive to the yellow-green-blue range. The human eye is also more sensitive to objects in motion than to still objects.

在有损压缩中，压缩的数据是不属于人类敏感范围的数据或包含大量运动的数据。两种常用的有损压缩技术是 JPEG 和 MPEG。这些技术及其变体将在本章和下一章中进行描述。

In lossy compression, the data compressed is the data that does not fall within the human sensitivity range or data that contains a great deal of motion. Two commonly used lossy compression techniques are JPEG and MPEG. These techniques, and variations of them, are described in this and the next chapter.

数据缩减

Data Reduction

视频文件通常包含冗余，可用于减少要存储的数据量。这可以通过记录帧内 ( intraframe ) 和帧间 ( interframe ) 的差异而不是存储每个帧的所有信息来完成。

Video files generally contain redundancy that can be used to reduce the amount of data to be stored. This can be done by registering the differences within a frame (intraframe) and between frames (interframe) rather than storing all the information from each frame.

帧内压缩

Intraframe Compression

帧内压缩利用空间冗余或帧空间内的数据重复来定义可以丢弃的数据。这种压缩是通过一种称为子采样的技术实现的。在子采样中，通过仅存储构成图像的一些像素来减少描述图像所需的位数。例如，可以忽略一行中的每隔一个像素和每隔一行的整个像素。那些被保留的像素然后会增加大小以补偿被遗漏的数据（图 14.3）。

Intraframe compression utilizes spatial redundancy, or the repetition of data within the space of the frame, to define the data that can be discarded. This compression is achieved through a technique called sub-sampling. In sub-sampling, the number of bits needed to describe an image is reduced by storing only some of the pixels that make up the image. For instance, every second pixel in a row and the entirety of every second row could be ignored. Those pixels that are retained would then be increased in size to compensate for the data that has been left out (Figure 14.3).

另一种子采样策略使用一组像素的平均值。该平均值代替了这些像素的原始值。子采样有效地减少了图像中的像素数量。或者，不是减少图像中的像素数量，而是可以减少关于每个像素的信息量。然而，这也减少了图像中颜色和灰度的渐变数。

Another sub-sampling strategy uses the average values for a group of pixels. This average is substituted for the original values for those pixels. Sub-sampling effectively reduces the number of pixels in an image. Alternatively, rather than reduce the number of pixels in an image, the amount of information about each pixel can be reduced. This, however, also reduces the number of gradations of color and grays in the image.

图 14.3 帧内压缩

Figure 14.3 Intraframe Compression

量化是减少数据量的另一种方法。量化对要存储的值的范围和要编码的数据的值之间的增量设置了数量限制，从而压缩了需要存储的数据量。

Quantization is another method for reducing the amount of data. Quantizing sets a limit on the quantity for the range of values to be stored and the increments between values for the data to be coded, thereby compressing the amount of data needed to be stored.

变换编码使用复杂的转换过程将图像的编码块转换为压缩图像或视频文件以供存储或传输。

Transform coding uses a complex conversion process to turn coded blocks of the image into a compressed image or video file for storage or transmission.

帧间压缩

Interframe Compression

帧间压缩将连续帧的不变部分从一帧与另一帧进行比较。例如，物体在一帧与另一帧之间的简单移动或光线的变化，可以存储为帧之间的类似命令（图 14.4）。命令占用的存储空间少于存储完整帧所需的实际数据。帧间压缩使用一种子采样版本，其中并非所有帧都被传输。相反，存储命令以重新创建数据。帧间压缩中使用的其他策略是差分编码、基于块的差分编码和基于块的运动补偿。

Interframe compression compares the unchanging portions of successive frames from one frame to the other. Simple movements of objects between one frame and another or changes in light, for example, can be stored as similar commands between frames (Figure 14.4). The commands take up less storage than the actual data required to store the complete frame. Interframe compression utilizes a version of sub-sampling in which not all frames are transmitted. Instead, the commands are stored to recreate the data. Other strategies used in Interframe compression are difference coding, block-based difference coding, and block-based motion compensation.

在差分编码中，将每一帧与前一帧进行比较，并且仅存储那些发生变化的像素。

In difference coding, each frame is compared to the preceding one and only those pixels that are changed are stored.

图 14.4 帧间压缩

Figure 14.4 Interframe Compression

基于块的差异编码以相同的方式工作，但在块级别而不是像素级别。帧被分成像素块，帧之间比较的正是这些块。

Block-based difference coding works in the same fashion but at a block level rather than a pixel level. The frames are divided into blocks of pixels, and it is these blocks that are compared between frames.

基于块的运动补偿是差分编码的进一步改进。帧像以前一样被分成块。然后将这些块与前一帧中的块进行比较，以找到相似的块。如果相似块位于不同位置，则存储的是位置差异而不是块中的实际信息。

Block-based motion compensation is a further refinement of difference coding. The frame is divided into blocks as before. These blocks are then compared to blocks in the preceding frame to find blocks that are similar. If the similar blocks are in different locations, it is this difference of position that is stored rather than the actual information in the block.

进一步的改进是双向运动补偿，其中将当前帧与前后帧进行比较，并存储差异而不是帧的内容（帧内和帧间压缩将在下一章中更详细地讨论）。

A further refinement is bidirectional motion compensation, in which the current frame is compared to both the preceding and following frame and the differences stored rather than the content of the frame (intraframe and interframe compression are discussed in more detail in the following chapter).

数据传输限制

Data Transmission Limitations

节目源的要求以及所使用的传输和存储设备可能会限制您对压缩类型的选择。传输限制由传输和接收系统在给定时间段内可以处理的数据量控制。存储的限制是显然受到可用空间的限制。因此，数据压缩中要考虑的另一个因素是准确存储、传输和再现数据所需的比特率。

The requirements of the programming source, as well as the transmission and storage devices being used, may limit your choice of compression types. The limitations for transmission are controlled by the quantity of data the transmission and receiving systems can handle in a given time period. The limitations for storage are obviously limited by the space available. Therefore, another factor to be considered in data compression is the bit rate needed to store, transmit, and reproduce the data accurately.

比特率

Bit Rates

图像的复杂性是帧与帧之间的移动量或变化量与图像中包含的细节数量相结合的结果。为了及时保持适当的图像运动，组成数据的零和一或数字位必须足够快地传输和接收，以便在适当的时间范围内再现图像。根据图像的复杂性和所需的质量水平，使用不同的数据速率或比特率——即数据处理的速度。

The complexity of an image is a result of the combination of the amount of movement or change from frame to frame and the quantity of detail contained in the image. To maintain proper image motion in time, the zeros and ones, or digital bits, that comprise the data must be transmitted and received quickly enough to reproduce the image in the proper time frame. Depending on the complexity of the image and the required level of quality, different data rates, or bit rates—that is, the speed at which the data is processed—are used.

如果图像本质上不太复杂，或者如果所需的质量水平不高，则可以使用固定或恒定的数据速率或比特率。在图像更复杂或所需质量水平较高的情况下，可以使用可变比特率，以便在不影响质量的同时保持降低的数据速率。由于这些差异，恒定比特率可用于实时压缩图像，而可变比特率则不能。

If the images are less complex in nature, or if the required level of quality is not high, a fixed or constant data rate or bit rate may be used. Where the images are either more complex or the required level of quality is high, variable bit rates may be used in order to maintain a reduced data rate while not compromising the quality. Because of these differences, constant bit rates can be used to compress images in real time, whereas variable bit rates cannot.

恒定比特率

Constant Bit Rates

固定或恒定比特率(CBR) 会导致不同级别的图片质量，因为不允许图像复杂性。广播媒体（例如电缆、卫星和地面广播）要求其传输设备具有恒定的比特率。现场直播、卫星连接和未压缩视频的回放都需要在传输时立即进行实时压缩。

Fixed or constant bit rates (CBR) result in varying levels of picture quality because there is no allowance for image complexity. Broadcast media—such as cable, satellite, and terrestrial broadcasting—require constant bit rates for their transmission equipment. Live broadcasts, satellite linkups, and playback of uncompressed video all require immediate real-time compression while being transmitted.

可变比特率

Variable Bit Rates

尽管视频以固定帧速率运行，但编码每个帧所需的数据量可能会有所不同，具体取决于场景的复杂性。当图像的复杂性发生变化时，可变比特率(VBR) 可实现一致的图像质量。图像的每个部分都以其最佳压缩率进行分析和压缩。图像的不太复杂的部分以较高的速率压缩，而图像的较复杂的部分以较低的速率压缩。为了实现可变比特率，必须对图像内容进行更多分析，以用最少的数据量获得最好的质量；大多数编码软件和设备都进行二次编码可变比特率编码，第一次通过视频专门用于简单分析视频。对于可变比特率，编码过程更加复杂并且不能实时完成。VBR 编码用于存储在 DVD 等媒体中。

Although video runs at a fixed frame rate, the amount of data required to encode each frame can be variable, depending on scene complexity. Variable bit rates (VBR) allow for consistent picture quality when the complexity of the image varies. Each part of the image is analyzed and compressed at its optimal compression rate. Less complex portions of the image are compressed at higher rates while more complex portions of the image are compressed at lower rates. In order to achieve variable bit rates, there must be greater analysis of the image content to achieve the best quality with the least amount of data; most encoding software and equipment does two-pass variable bit rate encoding, with the first pass over the video devoted to simply analyzing the video. With variable bit rates, the encoding process is more complex and cannot be done in real time. VBR encoding is used for storage in media such as DVDs.

JPEG 压缩

JPEG Compression

JPEG 定义了压缩静止图像（例如图形和照片）的标准。与前面章节中讨论的视频标准组类似，JPEG 压缩是由联合图像专家组开发的，该专家组是国际标准化组织 (ISO) 和国际电工委员会 (IEC) 的联合工作组。

JPEG defines the standards for compressing still images, such as graphics and photographs. Similar to video standards groups discussed in previous chapters, JPEG compression was developed by the Joint Photographic Experts Group, a joint working group of the International Standardization Organization (ISO) and the International Electrotechnical Commission (IEC).

在 JPEG 压缩中，图像数据从 RGB 转换为亮度（Y 分量）和色度信息（色差信号、Cb 和 Cr 分量）。JPEG 利用人眼对亮度变化比对颜色变化更敏感的优势，通过对图像中的色度或颜色信息进行采样而不是对亮度进行采样。此过程称为下采样或色度二次采样。

In JPEG compression, the image data is converted from RGB into luminance (the Y component) and chrominance information (the color difference signals, the Cb and Cr components). JPEG takes advantage of the human eye’s greater sensitivity to changes in luminance than changes in color by sampling the chroma or color information in the image less often than the luminance. This process is known as downsampling or chroma subsampling.

下采样可以导致数据仅在水平方向减少 2 倍，或者如果同时使用，则在水平和垂直方向上减少 2 倍。然后将这些分量分组为 8 × 8 像素的块，并使用一种称为离散余弦变换或 DCT 的变换编码进行转换。通过使用帧内编码方法对图像中的冗余亮度信息进行编码，可以进一步减少数据。

Downsampling can result in data reduction by a factor of 2 in the horizontal direction only or by a factor of 2 in both the horizontal and vertical directions if both are used. The components are then grouped in blocks of 8 × 8 pixels and converted using a type of transform coding called Discrete Cosine Transform, or DCT. Data can be reduced further by encoding redundant luminance information in the image using intraframe coding methods.

10 比 1 的 JPEG 压缩导致图像看起来与原始图像没有变化。100 比 1 的更积极的压缩是可能的，但视觉退化是明显的。使用的压缩级别取决于图像文件的最终用途。

JPEG compression of 10 to 1 results in images that appear to be unchanged from the original. More aggressive compressions of 100 to 1 are possible, but visual degradation is apparent. The levels of compression used are dependent on the end use of the image file.

JPG 2000

JPEG 2000

JPEG 2000旨在处理比 JPEG 更高的压缩率，但不会引入在基于 DCT 的 JPEG 标准下更高压缩率的副产品。JPEG 2000 使用离散小波变换或 DWT，而不是离散余弦变换编码方法。DWT 方法不将图像分成块，而是分析整个图像并将图像数据组织成更容易压缩的形式。这减少了 DCT 引入的块效应。

JPEG 2000 was designed to handle higher compression ratios than can JPEG, but without introducing the artifacts that are a by-product of higher compression under the DCT-based JPEG standards. Instead of the Discrete Cosine Transform method of coding, JPEG 2000 uses Discrete Wavelet Transform, or DWT. The DWT approach does not divide the image into blocks but analyzes the whole image and organizes the image data to a more easily compressed form. This reduces the blocking artifacts introduced by DCT.

与 JPEG 一样，图像从 RGB 转换为亮度和色度（Y、Cb 和 Cr）信息。然后将图像平铺到单独编码的区域中。结果被称为子带，然后被量化并进一步处理成所谓的区域，它们是图像中大致相关的块。区域被分成大小相等的代码块，编码器对这些块进行编码（图 14.5）。

As with JPEG, the images are transformed from RGB to the luminance and chrominance (Y, Cb, and Cr) information. The image is then tiled into areas that are encoded separately. The results are called sub-bands, which are then quantized and further processed into what are called precincts, which are approximately related blocks in the image. The precincts are divided into code blocks that are of equal sizes, and the encoder codes these blocks (Figure 14.5).

这种编码分三个阶段进行，然后将生成的比特流分成数据包进行传输。那些包含最低有效位的数据包可以被丢弃。JPEG 2000 专为多媒体设备、视频流和视频服务器、高清卫星图像和视频序列存储等应用而设计。

This coding takes place in three stages and the resultant bit stream is then divided into packets for transmission. Those packets containing the least significant bits can be discarded. JPEG 2000 is designed for applications such as multimedia devices, video streaming and video servers, HD satellite imagery, and storage of video sequences.

动态 JPEG 压缩

Motion JPEG Compression

Motion JPEG或M-JPEG虽然未包含在 JPEG 标准中，但它是从 JPEG 发展而来的早期尝试，通过将每个图像视为单个静止图片来压缩运动图像。M-JPEG 压缩使用帧内编码，用于非线性编辑系统、某些 Internet 浏览器、游戏机和压缩视频磁盘。

Motion JPEG, or M-JPEG, while not covered by the JPEG standard, was developed from JPEG as an early attempt to compress moving images by treating each image as a single still picture. M-JPEG compression uses intraframe coding and is used in nonlinear editing systems, some Internet browsers, game consoles, and compressed video disks.

MPEG 压缩

MPEG Compression

MPEG压缩由运动图像专家组开发，定义了压缩运动图像的标准。MPEG 技术建立了压缩、编码和解码数据的协议，而不是编码方法本身。换句话说，规则规定了数据的顺序和数据必须包含的内容，而不是数据的方法

MPEG compression was developed by the Motion Picture Experts Group and defines the standards for compressing moving images. MPEG techniques establish the protocols for compressing, encoding, and decoding data, but not the encoding methods themselves. In other words, the rules dictate the order of the data and what the data must contain but not the method by which the data

图 14.5 离散小波变换 (DWT) 过程图 14.5

Figure 14.5 Discrete Wavelet Transform (DWT) Process Figure 14.5

是派生的。这允许不断改进编码技术，而不必不断改变现有设备。下一章将更深入地介绍 MPEG 压缩。

is derived. This allows for continuous improvement in encoding techniques without having to constantly change existing equipment. The following chapter takes a more in-depth look at MPEG compression.

其他压缩编解码器

Other Compression Codecs

许多其他压缩系统都基于 MPEG 和 JPEG。一些格式，如 HDV 和 XDCam，使用 MPEG 的工具集，但适用于特定用途。其他格式，如 H.264 或 AVC（高级视频编码），是 MPEG 格式，其名称基于其他标准组类别或由在 MPEG 协议内开发改进压缩格式的设备制造商进行营销。这些编解码器的下一代 H.265 或 HEVC（高效视频编码）能够将视频压缩成更小的文件，并能够处理更大帧的 4K 和 8K 图像。

Many other compression systems are based on MPEG and JPEG. Some formats, such as HDV and XDCam, use the toolsets of MPEG, but are adapted to specific uses. Other formats, such as H.264 or AVC (Advanced Video Coding), are MPEG formats with names based on other standards groups categories or marketing by equipment manufacturers who developed improved compression formats within the MPEG protocols. The next generation of these codecs, H.265 or HEVC (High Efficiency Video Coding) is able to compress video into smaller files and has the ability to work with the larger frames of 4K and 8K images.

压缩过程中引入的问题

Problems Introduced During Compression

在数字数据的压缩和编码过程中，图像中可能会出现各种错误和不准确之处。其中一些问题包括混叠、量化噪声、过载和退化。

During compression and encoding of digital data, various errors and inaccuracies can be introduced into the image. Some of these problems include aliasing, quantization noise, overload, and degradation.

当被数字化的频率对于采样频率来说太高时，就会发生混叠。混叠会产生由穿过图像的垂直线组成的失真。

Aliasing occurs when frequencies being digitized are too high for the sampling frequency. Aliasing produces a distortion consisting of vertical lines through the image.

量化噪声是由量化过程引起的，它迫使频率进入有限的固定数量的级别或步骤，从而在最终图像中产生粗糙度。

Quantization noise is caused by the quantization process, which forces the frequencies into a limited fixed number of levels or steps, producing coarseness in the final image.

如果信号幅度太大，就会发生过载。超过可以正确数字化的最大级别的所有级别都将转换为白色并生成漂白的最终图像。在另一种由低振幅信号引起的过载中，所有低于最小值的电平都将转换为黑色，从而导致最终图像变暗。

Overload occurs if the amplitude of a signal is too great. All levels exceeding the maximum level that can be correctly digitized are converted to white and produce a bleached final image. In another type of overload caused by low amplitude signals, all levels below a minimum are converted to black causing a darkened final image.

在压缩图像的传输过程中可能会发生降级。压缩过程的性质意味着单个比特错误会对最终图像产生更大的影响。

Degradation can occur during the transmission of the compressed images. The nature of the compression process means that a single bit error can have an exaggerated effect on the final image.

压缩伪影

Compression Artifacts

压缩和解压缩过程有时会在恢复的图像中引入小的可见错误。这些错误称为工件。伪像的类型取决于所使用的压缩类型和信号内容。

The compression and decompression process sometimes introduces small visible errors into the restored image. These errors are called artifacts. The type of artifact depends on the type of compression used and the signal content.

色度拖尾——由于亮度水平低或色度水平高，颜色可能会在芯片上的各个位置渗出。结果称为拖尾。外观是图像中区域之间颜色混合的外观。

Chrominance smear—As a result of low luminance levels or high chroma levels, colors can bleed across sites on a chip. The result is called smearing. The appearance is that of colors blending between areas in the image.

色度爬行——场景中非常精细的垂直条纹可以产生高频亮度信号，这些信号开始被解释为色度信息。这看起来像是条纹表面上闪烁的彩虹色。

Chrominance crawl—Very fine vertical stripes in a scene can produce high frequency luminance signals that start to be interpreted as chrominance information. This appears as a shimmer of rainbow colors over the striped surface.

块状— 这是看似平铺整个静止图像的小而规则的方块的外观。

Blocking—This is the appearance of small, regular squares that appear to tile an entire still image.

蚊子— 这是指视频压缩后可能出现在尖锐边缘周围的模糊点。

Mosquitoes—This refers to the fuzzy dots that can appear around sharp edges after video compression.

编解码器属性

Codec Attributes

图像处理中使用了数十种不同的编解码器，各有优缺点，这使得它们适用于视频制作阶段的不同任务。

There are dozens of different codecs in use in image processing, each having strengths and weaknesses, which make them suitable for different tasks in the stages of video production.

对于图像捕获，能够保留尽可能多的图像细节的编解码器是理想的选择。在这个早期阶段过度压缩会丢弃细节，这些细节会使后期处理（例如色彩校正和图像合成）变得更加困难。非常高端的相机通过从每个 RGB 通道捕获未压缩的数据来记录尽可能多的细节。这导致创建大量数据来存储和移动。

For image capture, a codec that preserves as much image detail as possible is ideal. Compressing too much at this early stage will discard detail that can make post processing—such as color correction and image compositing—more difficult. Very high-end cameras record as much detail as possible by capturing uncompressed data from each of the RGB channels. This leads to the creation of tremendous volumes of data to store and move.

在相机频谱的另一端，手机和廉价的消费类相机使用 H.264 等长 GOP 编解码器严重压缩信号。虽然这会创建非常易于管理的文件大小，但后期制作图像处理因缺乏保留的颜色深度和细节而受到限制。

At the other end of the camera spectrum, phones and inexpensive consumer cameras heavily compress the signal using long GOP codecs like H.264. While this creates very manageable file sizes, post production image processing is limited by the lack of color depth and detail that is retained.

后期制作编辑最好在帧内编解码器中完成。使用帧间技术的编解码器（例如 MPEG 和 H.264）需要对视频进行解码以找到要进行编辑的各个帧，然后即时对这些帧进行重新编码。这个过程甚至会对最强大的计算机编辑系统造成负担，并导致缓慢而令人沮丧的编辑体验。DN ´ HD 和 ProRes 等编解码器由编辑系统制造商设计来解决此问题。

Post production editing is best done in an intraframe codec. Codecs that use interframe techniques, such as MPEG and H.264, require decoding the video to find the individual frames to make an edit, then re-encoding the frames on the fly. This process can tax even the most powerful computer edit systems, and make for a slow and frustrating editing experience. Codecs such as DN ´ HD and ProRes are designed by edit system manufacturers to address this issue.

用于网络的视频需要在专为通过 Internet 传输数据而设计的编解码器中进行压缩。文件可以压缩得更重，长 GOP 编解码器是理想的（GOP 编解码器将在下一章中讨论）。H.264 经常被最好的选择，但网络上也有很多 Windows Media 格式和其他编解码器的内容。

Video destined for the web needs to be compressed in a codec that is designed for streaming the data over the Internet. The files can be more heavily compressed and long GOP codecs are ideal (GOP codecs are discussed in the following chapter). H.264 is frequently the best choice, but there is also much content on the web in Windows Media formats and other codecs as well.

从捕获到交付，图像可能会从一个编解码器移动到另一个编解码器，或者被转码多次。请记住，随着图像从压缩较少变为压缩较多，细节和色彩保真度会降低。一旦部分图像被丢弃以支持较小的文件大小，它们将无法恢复。从压缩率高的图像转换为压缩率低的格式不会改善图像。

From capture to delivery, an image may move from one codec to another, or be transcoded, several times. Keep in mind that as the images go from less compressed to more compressed, detail and color fidelity are reduced. Once parts of the image are discarded in favor of smaller file sizes, they cannot be recovered. Going from a heavily compressed image to a less compressed format does not improve the image.

MPEG 过程

The MPEG Process

MPEG 过程首先分析称为视频流的一系列视频帧。冗余信息被编码和压缩。然后将压缩视频流编码为比特流。然后以回放设备要求的比特率存储或传输比特流。数据在使用时被解码和解压缩，图像恢复到原来的形式。

The MPEG process starts by analyzing a sequence of video frames known as the video stream. Redundant information is encoded and compressed. The compressed video stream is then encoded into a bit stream. The bit stream is then stored or transmitted at the bit rate called for by the playback equipment. The data is decoded and uncompressed when it is to be used and the image restored to its original form.

MPEG 压缩结合了两种不同的压缩方案：空间和时间。空间压缩通过消除图像中的冗余数据来减少每个视频帧中包含的数据量。时间压缩比较图像之间随时间的变化，并存储仅代表变化的数据。

MPEG compression utilizes a combination of two different compression schemes, spatial and temporal. Spatial compression reduces the quantity of data contained in each frame of video by eliminating the redundant data within the image. Temporal compression compares the changes between the images over time and stores the data that represents only the changes.

空间压缩使用与上一章中描述的 JPEG 压缩相同的技术来创建帧内图片，称为I 帧。与时间压缩帧不同，I 帧是完整的“独立”图像，可以在不参考任何周围帧的情况下解码和显示。

Spatial compression uses the same technique as JPEG compression, described in the previous chapter, to create an intra picture, called an I frame. Unlike the temporal compression frames, the I frames are complete “stand-alone” images that can be decoded and displayed without reference to any surrounding frames.

I 帧散布在视频流中，并作为帧间时间压缩的参考。这种排列有点像栅栏，I 帧代表相对较少的栅栏柱，而时间帧代表许多栅栏。称为 B 帧和 P 帧的时间压缩帧包含描述 I 帧的不同区域在中间帧之间如何变化的运动信息。B 和 P 帧包含的数据远少于 I 帧。它们仅包含有关帧之间发生的更改的数据。这说明了 MPEG 编码的高效率。可以实现 25:1 的压缩率，而未压缩图像的质量几乎没有或没有明显下降。I帧以及B和P帧在下面更详细地描述。

The I frames are interspersed within the video stream and act as references for the temporal compression between frames. The arrangement is somewhat like a picket fence, with the I frames representing the relatively few fence posts while the temporal frames are the many pickets. The temporal compression frames, called B and P frames, contain motion information that describes how the different regions of the I frame have changed between the intervening frames. The B and P frames contain far less data than the I frames. They contain only the data about the changes that have occurred between frames. This accounts for the great efficiency of MPEG encoding. Compression rates of 25:1 can be achieved with little or no noticeable degradation in the quality of the uncompressed image. I frames and B and P frames are described in more detail below.

我帧

I Frames

I帧（帧内图片）是经过详细采样的完整图像的一帧，因此它可以用作周围帧的参考。每个 I 帧被分成 8 × 8 像素块，然后将其放置在称为宏块的 16 × 16 像素块组中 （图 15.1（图版 20））。然后使用各种压缩技术压缩这些宏块。I 帧根据需要经常创建，特别是当图像内容发生重大变化时。在典型的视频流中，这种情况大约每秒发生两次。

An I frame (intra picture) is one frame that is a complete image sampled in detail so it can be used as a reference for the frames around it. Each I frame is divided into 8 × 8 pixel blocks which are then placed in groups of 16 × 16 pixel blocks called macroblocks (Figure 15.1 (Plate 20)). These macroblocks are then compressed using a variety of compression techniques. I frames are created as often as needed and particularly when there is a substantial change in the image content. In a typical video stream, this occurs approximately two times per second.

图 15.1（图 20） I 帧宏块和块

Figure 15.1 (Plate 20) I Frame Macroblocks and Blocks

图片组 (GOP)

The Group of Pictures (GOP)

I、B 和 P 帧组合在一起形成图片组或 GOP。GOP 必须以 I 帧开始和结束，以允许将其用作周围 B 和 P 帧的参考。GOP 可以只包含 P 帧或在 I 帧之间同时包含 B 和 P 帧。可以增加 GOP 中 B 帧或 P 帧的数量 或减少，具体取决于压缩视频的图像内容或应用程序。例如，具有复杂内容（大量细节）的快速动作序列会使用较短的组，因此会使用更多的 I 帧。组长度通常在 8 到 24 帧之间。图 15.2显示了 30 帧 IBP 编码视频流的典型 GOP 结构。

I, B, and P frames are grouped together to form a Group of Pictures, or GOP. A GOP must start and end with an I frame to permit its use as a reference for the surrounding B and P frames. A GOP can contain just P frames or both B and P frames in between the I frames. The number of B frames or P frames within a GOP can be increased or decreased depending on image content or the application for which the compressed video is intended. For example, a fast-moving action sequence with complex content (lots of detail) would use shorter groups, hence more I frames. Group lengths typically range from 8 to 24 frames. Figure 15.2 shows the typical GOP structure for 30 frames of IBP-encoded video stream.

图 15.2 图片组 (GOP)

Figure 15.2 Group of Pictures (GOP)

知识产权法

IP Method

仅使用 I 和 P 帧就可以实现出色的压缩质量，即使 P 帧仅在时间上使用后向引用。以下示例显示了仅使用 I 和 P 帧编码的源视频素材的三帧（图 15.3）。

Excellent compression quality can be achieved using just I and P frames, even though the P frames only use backward references in time. The following example shows three frames of the source video material encoded only with I and P frames (Figure 15.3).

有创血压法

IBP Method

添加可选的 B 帧可提高压缩质量，但会降低数据传输速率。B 帧在时间上向前和向后看，因此具有最有用信息的帧可以用作参考（图 15.4）。

The addition of the optional B frame increases the compression quality but lowers the rate of data transmission. The B frame looks both forward and backward in time so the frame with the most helpful information can be used as a reference (Figure 15.4).

图 15.3 IP 压缩方法

Figure 15.3 IP Method of Compression

图 15.4 IBP 压缩方法

Figure 15.4 IBP Method of Compression

配置文件和级别

Profiles and Levels

I、B 和 P 工具可以组合成越来越复杂的压缩技术，称为配置文件。根据使用的配置文件，图片质量可以提高。根据使用的压缩工具和压缩视频的物理参数，例如图片大小、分辨率和比特率，每个配置文件都可以分为质量级别。有四个级别提供一系列图像质量，从有限清晰度（¼ 分辨率视频）到具有 1080 扫描线的高清。每个级别都有自己特定的输入视频标准，例如标清视频或高清视频。

The I, B, and P tools can be combined into progressively more sophisticated compression techniques called profiles. Picture quality can improve depending on the profile used. Each profile can be divided into levels of quality, depending on the compression tools used and the physical parameters of the compressed video, such as the picture size, resolution, and bit rates. There are four levels that provide a range of picture quality, from limited definition (¼ resolution video) to high definition with 1080 scan lines. Each level has its own specific standard for the input video, such as Standard Definition video or High Definition video.

主级别的主要配置文件

Main Profile at Main Level

可以混合和匹配不同的配置文件和级别，以创建各种图片大小、比特率和编码质量。标清图像最有用的组合是Main Level 的 Main Profile（缩写为MP@ML）。Main Profile是指可以使用I、B、P帧进行压缩，Main Level是指画面分辨率在NTSC制下为720×480。不同的存储、传送和传输系统具有不同的比特率约束。I、B、P 压缩工具非常灵活，MP@ML 可以调整比特率。降低比特率会降低图像质量，除非使用更复杂的编码工具进行补偿。

The different profiles and levels can be mixed and matched to create a wide variety of picture sizes, bit rates, and encoding qualities. The most useful combination for Standard Definition images is the Main Profile at Main Level (abbreviated as MP@ML). Main Profile means that I, B, and P frames can be used for compression, and Main Level means that the picture resolution is 720 × 480 in NTSC. Different storage, delivery and transmission systems have different bit rate constraints. The I, B, P compression tools are flexible enough that MP@ML can adjust the bit rates. Lowering the bit rate reduces the picture quality unless it is compensated for by using more sophisticated encoding tools.

高清配置文件和级别

High Definition Profiles and Levels

MPEG-2 也有许多专为高清图像设计的配置文件和级别组合。Main Profile at High Level 适用于两种高清格式，1920 × 1080 和 1280 × 720。ATSC 和 DVB 广播格式使用 MP@HL，但是色度被大量二次采样到 4:2:0，这代表了最低的数字颜色采样（颜色二次采样将在下一节中讨论）。

MPEG-2 has a number of Profile and Level combinations designed for High Definition images as well. Main Profile at High Level is for the two HD formats, 1920 × 1080 and 1280 × 720. ATSC and DVB broadcast formats use MP@HL, however the chroma is heavily subsampled to 4:2:0, which represents the lowest digital color sampling (color subsampling is discussed in the following section).

MPEG-2 配置文件和级别中压缩最少的是高级 422 配置文件。这允许对高达 1920 × 1080 的图像进行 4:2:2 采样。允许高达每秒 300 兆位的数据速率。一些照相机和录像机制造商使用这种格式。例如，每秒 50 兆位的 Sony XDCAM 是 422P@HL。

The least compressed of the MPEG-2 Profiles and Levels is 422 Profile at High Level. This allows for 4:2:2 sampling of images up to 1920 × 1080. Data rates of up to 300 megabits per second are allowed. Several camera and recorder manufacturers use this format. For example, Sony XDCAM @ 50 megabits per second is 422P@HL.

在撰写本书时，MPEG-2 标准不允许帧大小大于 1920 x 1080 或帧速率高于每秒 60 帧。对于 4K 和 UHD 应用程序，必须使用其他压缩格式。最新的压缩标准 MPEG-4 允许更大的帧大小。即使是 HEVC（或 H.265）的最新发展也使其有可能成为更大帧的 MPEG 的继任者。

As of the writing of this book, the MPEG-2 standard does not allow frame sizes greater than 1920 x 1080 or frame rates above 60 frames pre second. For 4K and UHD applications, other compression formats must be used. The more recent compression standard, MPEG-4, allows for larger frame sizes. Even the recent development of HEVC (or H.265) makes it the likely successor to MPEG for larger frames.

颜色子采样

Color Subsampling

压缩过程的另一个方面是颜色子采样。如上所述，4:2:0和4:2:2是代表数字采样标准的数字。首先，RGB 通道被转换为亮度 (Y) 和两个色度通道（Cr 和 Cb）。将 RGB 视频信号转换为亮度和色度数据后，可以压缩色度部分，图像质量几乎没有明显损失。

Another aspect of the compression process is color subsampling. As mentioned above, 4:2:0 and 4:2:2 are numbers that represent digital sampling standards. First, the RGB channels are converted into luminance (Y) and two chrominance channels (Cr and Cb). After converting RGB video signals into luminance and chrominance data, the chrominance portion can be compressed with little apparent loss in image quality.

让我们考虑四种不同的视频数字化方案：4:4:4、4:2:2、4:1:1 和 4:2:0。在每种情况下，对于扫描线上的每组四个像素，亮度通道有四个数字样本。然而，这些方案的不同之处在于对每行中的色度进行采样的次数。例如，在 4:2:2 方案中，两个色度通道中的每一个只取两个样本（图 15.5（图 21））。每个色度样本由两个像素共享。结果，两个色度通道以亮度通道分辨率的一半数字化，将这两个通道的数据量减少了 50%。这将每帧视频所需的总数据减少了 33%。

Let’s consider four different digitizing schemes for video: 4:4:4, 4:2:2, 4:1:1 and 4:2:0. In each case, for every set of four pixels on a scan line, there are four digital samples of the luminance channel. The schemes differ, however, in the amount of times the chroma in each line is sampled. In the 4:2:2 scheme, for example, only two samples are taken for each of the two chrominance channels (Figure 15.5 (Plate 21)). Each chrominance sample is shared by two pixels. As a result, the two chrominance channels are digitized at half the resolution of the luminance channel, reducing the amount of data for those two channels by 50%. This reduces the total data required for each frame of video by 33%.

4:2:0 采样比 4:2:2 进一步采用了对色度通道进行子采样的想法。如果对于每四个像素，有四个亮度样本但没有色度样本，那就是 4:0:0 采样。当然，如果没有色度数据，您只会得到黑白图片。然而，如果 每隔一条扫描线以 4:2:2 数字化，中间的线以 4:0:0 数字化，来自 4:2:2 扫描线的色度数据可以由交替的 4:0:0 共享扫描线，进一步减少描述视频帧所需的数据量。

4:2:0 sampling takes the idea of sub-sampling the chrominance channels a step further than 4:2:2. If, for every four pixels, there were four samples of luminance but no samples of chrominance, that would be 4:0:0 sampling. Of course, with no chrominance data you would only have a black and white picture. However, if every other scan line was digitized at 4:2:2 and the lines in-between were digitized at 4:0:0, the chrominance data from the 4:2:2 scan lines could be shared by the alternating 4:0:0 scan lines, further reducing the amount of data required to describe a frame of video.

图 15.5（图 21） 颜色子采样

Figure 15.5 (Plate 21) Color Subsampling

图 15.5说明了 4:2:0 采样如何在每条扫描线上在 4:2:2 和 4:0:0 采样之间交替。因此，每个色度样本由水平方向的两个像素以及垂直方向的两条扫描线共享。这意味着色度样本覆盖 2 ´ 2 区域，或四个像素。因此，两个色度通道各只有亮度通道数据的 25%。将两个通道的数据要求降低到 25% 可将每个视频帧所需的总数据减少 50%。4:4:4 表示所有三个信号的副载波频率的四倍，并且 4:4:4:4 添加键信号或 alpha 通道作为数字信息的一部分。

Figure 15.5 illustrates how 4:2:0 sampling alternates between 4:2:2 and 4:0:0 sampling on each scan line. Each chrominance sample is therefore shared by two pixels horizontally as well as two scan lines vertically. This means that the chrominance samples cover a 2 ´ 2 area, or four pixels. As a result, the two chrominance channels each have only 25% of the data that the luminance channel has. Reducing the data requirements for two channels to 25% reduces the total data required for each frame of video by 50%. 4:4:4 represents four times the subcarrier frequency for all three of the signals and 4:4:4:4 adds the key signal, or alpha channel, as part of the digital information.

MPEG 变体

MPEG Variations

随着时间的推移，使用不同的压缩方案开发了 MPEG 变体，例如 MPEG-1、MPEG-2、MPEG-4。例如，MPEG-2 压缩可以使用各种计算机算法或数学公式来压缩图像。这些不同的算法可以组合使用，以在不损失质量的情况下提供逐渐增加的压缩。不同的 MPEG 压缩技术或变体更适合特定的应用。

Over time, MPEG variations, such as MPEG-1, MPEG-2, MPEG-4, were developed with different compression schemes. For example, MPEG-2 compression can use a variety of computer algorithms, or mathematical formulas, to compress the images. These different algorithms can be used in combination to provide progressively increased compression without loss of quality. Different MPEG compression techniques or variations lend themselves better to specific applications.

以分贝为单位测量音量

Measuring Volume as Decibels

人耳对显着范围的声音振幅或响度有反应。音频的赤裸感知（可能是手指轻轻拂过头发）与疼痛阈值之间的差异大约为 10 万亿比 1。因为这个范围是如此之大，所以必须创建一个测量系统来将这个信息范围缩小到更易于管理的数字。在数学中，对数通常用于简化大型计算。对数可以与任何数字系统一起使用，例如以 10 为底或以 2 为底。当对数使用十进制或以 10 为底数以简化声音测量时，该测量称为分贝。所有声音都以分贝为单位进行测量，并且所有测量值都是对数函数。

The human ear responds to a remarkable range of sound amplitude, or loudness. The difference between the bare perception of audio, perhaps fingers lightly brushing away hair, and the threshold of pain is on the order of a 10 trillion to 1 ratio. Because this range is so enormous, a measuring system had to be created that reduced this range of information to more manageable numbers. In mathematics, logarithms are often used to simplify large calculations. Logarithms can be used with any numeric system, such as base 10 or base 2. When logarithms use the decimal system, or base 10, to simplify the measurement of sound, that measurement is referred to as decibels. All sound is measured in decibels and all measurements are logarithmic functions.

分贝测量是多年前由贝尔实验室开发的，当时贝尔实验室是贝尔电话公司的一个部门。分贝记为dB。一分贝是一贝尔的十分之一，以亚历山大·格雷厄姆·贝尔的名字命名。但是，很少使用这种较大的计量单位 bel。

The decibel measurement was developed many years ago by Bell Laboratories, which was then a division of the Bell Telephone company. Decibels are notated as dB. One decibel is one tenth of one bel, which was named after Alexander Graham Bell. However, this larger unit of measurement, bel, is rarely used.

分贝不是一个具体的度量单位，就像一英寸或英尺是距离的精确度量单位一样。分贝实际上是测量信号与 0 dB 参考点之间的比率。（因数 10 乘以对数得到的是分贝而不是贝尔。）研究发现，在实验室条件下，大约 1 分贝是正常人耳可察觉的声音强度差异。在分贝标度的极低端，刚好高于 0 dB，是最小的可听声音，称为声音阈值。比 0 分贝强 10 倍的声音是 10 分贝，比 10 分贝强 100 倍的声音是 20 分贝（图 16.1）。

The decibel is not a specific measurement in the way that an inch or foot is an exact measurement of distance. A decibel is actually the ratio between a measured signal and a 0 dB reference point. (The factor of 10 multiplying the logarithm makes it decibels instead of bels.) It was found that, under laboratory conditions, about one decibel is the just-noticeable difference in sound intensity for the normal human ear. On the very low end of the decibel scale, just above 0 dB, is the smallest audible sound referred to as the threshold of sound. A sound 10 times more powerful than 0 dB is 10 dB, and a sound 100 times more powerful than 10 dB is 20 dB (Figure 16.1).

电子音频信号

Electronic Audio Signals

对于声学或声学工程师来说，0 dB 参考点是听力的阈值。对于电子产品，0 dB 参考点是传输音频信号的最大允许功率。因此，0 dB 测量指的是声学中与电子学中非常不同的声级，并且需要不同的测量标度。

For acoustics or acoustical engineers, the 0 dB reference point is the threshold of hearing. For electronics, the 0 dB reference point is the maximum allowable power for a transmitted audio signal. Therefore, a 0 dB measurement refers to a very different level of sound in acoustics than it does in electronics, and a different measuring scale is required.

图 16.1 以分贝为单位的噪音水平

Figure 16.1 Noise Levels in Decibels

声学工程师使用称为分贝声压级或dBSPL 的声学测量系统。声学声音的测量基于气压。电子音频信号基于电气测量系统。此比例使用体积单位测量或VU。持续传输的音频信号的最大允许强度为 0 dBVU。对于模拟电子录音，允许音频信号瞬间超过 0 dBVU +12 dB（图 16.2（图 22））。

Acoustic engineers use an acoustic measuring system called decibel sound pressure level or dBSPL. The measurement of acoustic sound is based on air pressure. Electronic audio signals are based on an electrical measuring system. This scale uses a volume unit measurement, or VU. The maximum allowable strength for a sustained transmitted audio signal is 0 dBVU. For analog electronic recording, it is permissible to have audio signals that momentarily exceed 0 dBVU by as much as +12 dB (Figure 16.2 (Plate 22)).

数字记录是数字数据的串行流。因为这个数字流代表了音频信号的各个方面，包括频率和幅度，所以 dBVU 的增加或减少 不会增加信号质量。数字录音的峰值通常在 –12 dB 范围内。在数字领域，0 dBFS（或 0 dB 满刻度）是指所有位都设置为 1 并表示最大信号（图 16.2）。与模拟音频不同，超过 0 dB 电平的数字信号会被削波并失真。

Digital recording is a serial stream of digital data. Because this digital stream represents every aspect of the audio signal, including frequency and amplitude, increases or decreases in dBVU do not add to the quality of the signal. Digital audio recordings are generally made to peak around the –12 dB range. In the digital realm, 0 dBFS, (or 0 dB full scale) is when all the bits are set to 1 and represent the maxium signal (Figure 16.2). Unlike analog audio, digital signals that exceed 0 dB level are said to clip and will be distorted.

图 16.2（图 22） 模拟 VU 表和数字音频表

Figure 16.2 (Plate 22) Analog VU Meter and Digital Audio Meter

数字音频

Digital Audio

录制视频信号时，音频部分作为串行数字流的一部分包含在视频中。数字音频信号有几个好处。因为噪声是模拟信息，所以记录为数字数据的音频不受模拟噪声问题的影响。此外，作为串行数字流，数字音频允许以更大的动态和频率范围进行记录和再现。

When recording a video signal, the audio portion is included with the video as part of the serial digital stream. A digital audio signal has several benefits. Because noise is analog information, audio recorded as digital data is immune to analog noise problems. Also, as a serial digital stream, digital audio allows for recording and reproducing with a greater dynamic and frequency range.

由于数字音频在信号数据流中，因此不需要单独的音频连接。一种称为 SDI（串行数字接口）的连接传输串行数据，包括音频、视频、同步、时间码等。音频通道数不受设备或物理录制过程的限制。数字音频通道数量的唯一限制是处理速度和可用带宽。

Since digital audio is in the stream of signal data, no separate audio connections are required. One connection, referred to as SDI (Serial Digital Interface), carries the serial data that includes audio, video, synchronizing, time code, and so on. The number of audio channels is not limited by the equipment or the physical recording process. The only limitation in the number of digital audio channels is the processing speed and the available bandwidth.

采样率

Sampling Rates

响度（以 dB 为单位）并不是需要了解的声音的唯一方面。同样重要的是你听到的声音的频率。人类仅对频谱的某些区域敏感。耳朵能够听到 20 至 20,000 赫兹或 20 kHz（千赫兹）之间的声音。

Loudness, as measured in dB, is not the only aspect of sound that needs to be understood. Equally important is the frequency of the sounds you hear. Human beings are sensitive to only certain areas of the frequency spectrum. The ear is capable of hearing between 20 and 20,000 Hz, or 20 kHz (kilohertz).

将模拟声音频率捕获为数据的过程称为采样。描述我们必须多久采样一次音频的定理以第 11 章讨论的美国物理学家哈里·奈奎斯特 (Harry Nyquist) 的名字命名。该定理指出，正弦波的采样必须略高于最高频率的两倍才能成功再现。如果采样率等于或小于原始频率，数据将在波形的某些点丢失。再现的信号将是不完整的（图 16.3）。

The process of capturing analog sound freqencies as data is called sampling. The theorem that describes how frequently we must sample audio is named after Harry Nyquist, the American physicist discussed in Chapter 11. The theorem states that sampling of a sine wave has to be slightly more than twice the highest frequency in order to be successfully reproduced. If the sampling rate is equal to or less than the original frequency, data will be lost at certain points along the wave. The reproduced signal will be incomplete (Figure 16.3).

图 16.3 奈奎斯特定理

Figure 16.3 Nyquist Theorem

根据 Nyquist 定理，音频的采样率必须略高于 40 kHz，或每秒 40,000 个样本。高质量音频的原始采样率设置为 44.1 kHz。为了使采样率在国际上同样有效 视频帧速率，专业视频设备选择 48 kHz。对于某些应用，采样率可以提高到 96 kHz 和高达 192 kHz。其他质量较低的应用程序可以通过首先滤除模拟信号的高频分量来降低音频采样率。低至 8 kHz 的采样率可用于“电话质量”录音。

Based on the Nyquist theorem, the sampling rate for audio had to be slightly more than 40 kHz, or 40,000 samples per second. The original sampling rate for high quality audio was set at 44.1 kHz. In order to have a sample rate that worked equally across international video frame rates, 48 kHz was chosen for professional video equipment. For some applications, the sampling rate can be increased to 96 kHz and as high as 192 kHz. Other, lower quality applications can reduce the audio sampling rate by first filtering away the high frequency component of the analog signal. Sample rates as low as 8 kHz can be used for “phone quality” recordings.

每个采样都由数字位组成。样本中包含的位数可能会有所不同。样本可以由 8 位、16 位、20、24 或 32 位等组成。样本中的位数越多，或使用的数字字越大，再现越真实。采样频率和样本中包含的位数仅受带宽和创建或再现数据的设备速度的限制。

Each sample taken is composed of digital bits. The number of bits contained in the sample can vary. A sample can be composed of 8 bits, 16 bits, 20, 24, or 32 bits, and so on. The more bits in the sample, or the larger the digital word used, the truer the reproduction. Both the frequency of sampling and the number of bits contained in the sample are restricted only by the band-width and the speed of the equipment creating or reproducing the data.

音频压缩

Audio Compression

采样是数字化过程的一部分。音频和视频一样，一旦被数字化或采样，就可以被压缩。压缩过程通过减少冗余信息来减少数据量。在人的听觉范围内——20 Hz 到 20 kHz——2 到 5 kHz 的范围，也就是人声的范围，是最敏感的。在压缩过程中，这个范围被赋予更高比例的压缩音频数据流。高于和低于此范围的频率被压缩得更多，并且分配给数据流的比例更小。

Sampling is part of the digitizing process. Audio, like video, once it is digitized or sampled, can be compressed. The compression process reduces the quantity of data by reducing redundant information. Within the range of human hearing—20 Hz to 20 kHz—the range of 2 to 5 kHz, which is the range of the human voice, is most sensitive. During the compression process, this range is given a higher proportion of the compressed audio data stream. Frequencies above and below this range are more heavily compressed and are allotted a smaller percentage of the data stream.

音频通常被压缩大约十比一。与视频压缩一样，根据所需的音质以及可用的带宽和采样率，使用不同的音频压缩技术。MPEG 压缩过程很常见。在 MPEG 压缩过程中，使用了三种数据速率。这些数据速率中的每一个都称为一个层。 层是一种数据传输速率，它基于每秒的样本数和该样本中包含的位数。这些层中的每一层都代表不同的再现质量。每一层都与其下面的层兼容。换句话说，Layer 1 可以复制 Layer 2 和 Layer 3。Layer 2 可以复制 Layer 3，但它们不向后兼容。

Audio is typically compressed by a factor of about ten to one. As with video compression, different audio compression techniques are used depending on the sound quality desired and the bandwidth and sampling rates available. The MPEG process of compression is common. Within the MPEG compression process, three data rates are used. Each of these data rates is referred to as a layer. A layer is a data transfer rate that is based on the number of samples per second and the number of bits contained in that sample. Each of these layers represents a different quality of reproduction. Each layer is compatible with the layer below it. In other words, Layer 1 can reproduce Layer 2 and Layer 3. Layer 2 can reproduce Layer 3, but they are not backward compatible.

第 1 层是最低压缩率，从而产生原始信号的最佳保真度。比特率为每通道每秒 192 千比特 (kbps)。

Layer 1 is the lowest rate of compression, thereby yielding the best fidelity of the original signal. The bit rate is 192 kilobits per second (kbps), per channel.

第 2 层是中等压缩率。比特率为每通道 128 kbps。在立体声中，两个通道组合的总目标速率为每秒 250 kbps。

Layer 2 is a mid-range rate of compression. The bit rate is 128 kbps per channel. In stereo, the total target rate for both channels combined is 250 kbps per second.

第 3 层是最高压缩率，每通道 64 kbps。第 3 层使用复杂的编码方法以最小的比特率获得最大的音质。这是通常称为MP3 的标准，代表 MPEG-2 音频第 3 层。

Layer 3 is the highest rate of compression at 64 kbps per channel. Layer 3 uses complex encoding methods for maximum sound quality at minimum bit rate. This is the standard popularly referred to as MP3, which represents MPEG-2 Audio Layer 3.

降噪

Noise Reduction

磁带上的模拟录音会产生固有的高频嘶嘶声。这是由于磁带运动时氧化物颗粒在音频磁头上移动造成的。颗粒在音频磁头上摩擦会产生嘶嘶声，有点像在木头上摩擦砂纸。噪音是由物理产生的现象，而不是记录的信号。这是记录介质的性质。

Analog recording on tape created an inherent high frequency hiss. This is caused by the movement of the oxide particles across the audio heads while the tape is in motion. The particles rubbing on the audio heads create a hissing sound, some-what like rubbing sandpaper on wood. The noise is created by a physical phenomenon and is not a recorded signal. It is the nature of the recording medium.

Ray Dolby 开发了模拟录音的降噪过程，他是一位工程师，他也参与了录像带录音的原创创作。杜比发现了构成这种高频嘶嘶声的频率范围。他确定，通过放大录制信号中的高频，然后将这些信号衰减或降低到播放时的原始电平，可以减少模拟磁带录音中固有的高频噪声。如果在没有放大的第一步的情况下在播放时简单地降低高频，则信号中的高频将会丢失。杜比编码可用于磁带上任何类型的模拟录音。

A process of noise reduction in analog recordings was developed by Ray Dolby, an engineer who was also involved in the original creation of videotape recording. Dolby discovered the range of frequencies that comprise this high frequency hiss. He determined that by amplifying the high frequencies in the recorded signal, and then attenuating or reducing those signals to their original levels on playback, the high frequency noise inherent in analog tape recordings could be reduced. If the high frequencies were simply reduced on playback without the first step of amplification, the high frequencies in the signal would be lost. Dolby encoding can be used for any type of analog recording on tape.

单声道、立体声和环绕声音频

Single-Channel, Stereo, and Surround Sound Audio

无论声音是如何录制、压缩或重放的，其被听到的方式取决于所使用的录音技术。例如，单声道或单声道音频，也称为单声道或单声道，由单个音频信号组成，不涉及左、右、前或后。回放时，单声道音频不会传递有关声音方向或深度的信息。

No matter how sound is recorded, compressed, or reproduced, how it is heard depends on the recording technique that is used. For example, single channel or mono audio, also called monophonic or monaural, consists of a single audio signal without reference to left, right, front, or rear. When played back, mono audio imparts no information as to the direction or depth of the sound.

其他音频记录系统，例如立体声和环绕声，包括传递有关声音方向和深度的信息的数据。立体声具有独立的左声道和右声道，更接近于通常听到声音的方式。由于耳朵在头部两侧的位置，每只耳朵接收声音的时间略有不同，从而使大脑能够定位声音的来源。对于立体声录音，声音是分开的，这样每只耳朵都能以自然的方式听到声音，给人一种深度和真实感。

Other audio recording systems, such as stereo and surround sound, include data that imparts information as to the direction and depth of the sound. Stereo, with discrete left and right channels, more closely resembles the way sound is normally heard. Due to the position of the ears on either side of the head, each ear receives the sound at a slightly different time, allowing the brain to locate the source of the sound. With stereo recordings, the sound is separated so that each ear hears the sound in a natural way, lending a sense of depth and reality.

为了增强这种逼真的效果，杜比实验室开发了环绕声。环绕声增加了出现在听众身后的额外声道。这些被称为环绕声道。术语环绕声是杜比实验室的商标。

To enhance this realistic effect, Dolby Labs developed surround sound. Surround sound adds additional channels that appear behind the listener. These are called the surround channels. The term surround sound is a trademark of Dolby Laboratories.

杜比数字和环绕声

Dolby Digital and Surround Sound

ATSC 为数字电视的视频部分采纳了一套标准，称为文件 A/53，在本书第 12 章中介绍。与 A/53 相关的标准表不涉及音频。音频标准在称为 A/52 的文件中设定。在 A/52 文件中，ATSC 将杜比数字编码系统称为 AC-3。AC-3 音频编码方法已被制造商接受为用于大多数消费设备的主要音频编码方法。因此，广播公司和制造商已接受此标准用于制作目的。

The ATSC adopted a set of standards for the video portion of digital television known as document A/53, introduced in Chapter 12 of this book. The table of standards associated with A/53 does not address audio. Audio standards are set in a document referred to as A/52. Within the A/52 document, the ATSC refers to the Dolby Digital coding system as AC-3. The AC-3 method of coding audio has been accepted by manufacturers as the primary audio coding method to be used for most consumer equipment. Consequently, broadcasters and manufacturers have accepted this standard for production purposes.

杜比数字 (Dolby Digital) 或 AC-3 涵盖了多种不同的音频输入、输出以及与多声道音频系统相关的各种声道。由于大多数制造商都采用杜比数字作为其制造标准，因此大多数新的消费设备都包含杜比数字解码器。因此，专业设备制造商设计和制造音频设备以适应杜比数字 AC-3 音频标准。

Dolby Digital, or AC-3, covers many different variations of audio inputs, outputs and the various channels associated with multi-channel audio systems. As most manufacturers have adopted Dolby Digital as their manufacturing standard, most new consumer equipment contains Dolby Digital decoders. Because of this, professional equipment manufacturers design and build audio equipment to accommodate the Dolby Digital AC-3 audio standard.

由于数字数据允许包含比模拟数据更多的信息，因此添加了更多音频通道以进一步增强音频的真实感。频道数量首先增加到六个。这称为 5.1 杜比数字，或简称为 5.1。

As digital data allows for the inclusion of more information than was possible in analog, more channels of audio have been added to further enhance the realism of the audio. The number of channels first was increased to six. This is referred to as 5.1 Dolby Digital, or just 5.1.

5.1 系统有五个独立的全频通道和一个用于低频低音的第六通道。剩下五个完整的频道， 右前、中、左、右后（图16.4）。前左声道和右声道相当于原始立体声声道，中间相当于原始单声道，左右后方相当于原始环绕声声道。然而，这些频道现在携带更多的音频数据，增加了节目音频部分的真实感。它们不再像旧的模拟系统那样受到限制。这些通道现在包含音频数据，可产生身临其境的效果。

The 5.1 system has five discrete, full-range channels and a sixth channel for low frequency bass. The five full channels are left and right front, center, and left and right rear (Figure 16.4). The front left and right channels would be the equivalent of the original stereo channels, the center the equivalent of the original mono channel, and the left and right rear the equivalent of the original surround channel. However, these channels now carry far more audio data that adds to the realism of the audio portion of a program. They are no longer as restricted as the older analog systems were. These channels now contain audio data that create an effect of being within the actual environment.

图 16.4 环绕声扬声器布局

Figure 16.4 Surround Sound Speaker Layout

第六个通道称为LFE通道，或低频效果通道。由于低频音频是非定向的，因此 LFE 扬声器的放置并不重要。低的频率音频，因为它的功率即使在低音量水平下，也往往会从表面反射，因此人耳无法辨别它的方向。由于 LFE 通道只需要其他全音频通道带宽的十分之一左右，因此它被指定为 .1 通道或通道的十分之一，从而指定 5.1 通道音频。

The sixth channel is referred to as the LFE channel, or Low Frequency Effects channel. Because low frequency audio is non-directional, the placement of the LFE speaker is not critical. Low frequency audio, because of its power even at low volume levels, tends to reflect off surfaces and so its direction is not discernible by the human ear. As the LFE channel needs only about one-tenth the bandwidth of the other full audio channels, it has been designated as .1 channel or a tenth of a channel, thereby giving the designation 5.1 channels of audio.

由于创建和录制的所有这些可能性，必须仔细指定和记录音频通道及其用途。视频节目磁带或文件可能具有单声道、立体声或多声道环绕声。环绕声可能是离散通道，或者使用模拟或数字编码进行编码。许多程序可能附加了不止一种格式的音频。例如，通常有六个独立的环绕声通道和两个带有立体声混音的附加通道。

With all these possibilities for creating and recording, the audio channels and their uses must be designated and documented carefully. A video program tape or file may have mono, stereo or multichannel surround. The surround might be discrete channels, or be encoded with either analog or digital encoding. Many programs may have more than one format of audio attached. For example, it is common to have six discrete channels for surround, and two additional channels with a stereo mix.

作为更身临其境的影院观看体验的一部分，可以增加环绕声道的数量。为了进一步扩展声场，7.1 声道系统在听者的左右两侧增加了两个额外的扬声器位置。

As part of the drive for more immersive and theatrical viewing experiences, the number of surround channels can be increased. To expand the sound field even further, the 7.1 channel system adds two additional speaker positions to the left and right of the listener.

异相音频

Out-of-Phase Audio

与任何基于正弦波的信号一样，音频信号的波可以彼此异相。如果波的相位相差 180º，或者换句话说，彼此正好相反，则会发生抵消。当一个波处于其峰值时，另一个将处于其低点（图 16.5）。结果将是沉默或接近 安静。单独听任何一方听起来都不错，因为需要两个信号来产生异相情况。小于 180º 异相的信号也会导致音量或振幅降低，但程度较小。

As with any signal based on sine waves, the waves of audio signals can be out of phase with each other. If the waves are 180º out of phase or, in other words, exactly opposite each other, cancellation will take place. When one wave is at its peak, the other would be at its low point (Figure 16.5). The result would be silence or near silence. Either side listened to alone would sound fine, as two signals are needed to create an out-of-phase situation. Signals less than 180º out of phase also cause a decrease in volume or amplitude but to a lesser degree.

图 16.5 异相音频

Figure 16.5 Out-of-Phase Audio

相位差情况可以通过相位计、示波器或有时仅通过聆听来检测。先听一边，然后听另一边，然后同时听两边，有时会发现不同步的情况。当同时收听两侧时，振幅下降将表明信号异相。

Out-of-phase situations can be detected by a phase meter, a scope, or sometimes just by listening. Listening to one side, then the other, and then both at once, will sometimes allow the detection of an out-of-phase situation. A drop in amplitude, when the two sides are listened to at once, will be an indication that the signals are out of phase.

异相错误可能发生在音频链的任何地方，从原始录音中的麦克风放置到最终回放。音频可能是异相录制的，或者扬声器接线不正确。纠正这个问题有时就像将信号路径一侧的两条线倒转一样简单。通过仅反转一侧，两个然后双方将彼此同步。可以在音频路径的任何位置进行此切换，问题将得到纠正。

The out-of-phase error can occur anywhere along the audio chain, from the microphone placement in the original recording to the final playback. The audio may have been recorded out of phase or the speakers may have been wired incorrectly. Correcting this problem can sometimes be as simple as reversing two wires on one side of the signal path. By reversing one side only, the two sides would then be in phase with each other. This switch can be made anywhere along the audio path, and the problem will be corrected.

如果音频被异相录制，则只能通过以正确的相位关系重新录制音频来纠正。可以播放异相音频，并通过反转信号路径的一侧来校正相位以用于播放目的。

If the audio is recorded out of phase, this can only be corrected by re-recording the audio in the correct phase relationship. It is possible to play back out-of-phase audio and, by phase reversing one side of the signal path, correct the phase for playback purposes.

一些数字示波器具有检查立体声音频的选项。如果 SDI 流中存在音频，信号将出现在示波器上。如果音频是立体声且同相，它将显示为一条直线对角线。如果音频异相，则两条线会按照它们异相的量分开显示。

Some digital scopes have a selection for checking stereo audio. If audio is present in the SDI stream, the signal will appear on the scope. If the audio is stereo and in phase, it will appear as a straight diagonal line. If audio is out of phase, the two lines appear separated by the amount they are out of phase.

测量音频相位

Measuring Audio Phase

一些数字示波器可以选择使用称为利沙如图形的显示来检查立体声音频。如果音频是同相的，它会出现在示波器上标记为“同相”的轴上（图 16.6（图 23））。如果音频异相，它会倾向于指向与同相线成 90º 的轴。通道之间的差异越大（或内容越立体），显示就越混乱。对于非常不同的材料，很难确定示波器上的信号是同相还是异相。

Some digital scopes have a selection for checking stereo audio using a display called a lissajous pattern. If the audio is in phase, it will appear to orient along an axis on the scope marked “in phase” (Figure 16.6 (Plate 23)). Should the audio be out of phase, it will tend to orient to the axis that is 90º to the in-phase line. The greater the difference between the channels (or the more stereo the content), the more confused the display appears. It is difficult with very different material to be certain if the signal is falling in or out of phase on the scope.

图 16.6中示波器的第二个特征显示了另一个有用的相位工具。这有助于确定具有非常不同内容的立体声音频的相位。该功能称为相关性仪表，由菱形表示。在图中显示的显示屏上，有 5 个不同的相关性仪表（显示为菱形）， 一个在每对立体声仪表下方，一个在信号的利沙如显示下方。菱形指示器显示测量的立体声对中的通道相似或相关的程度。如果它们完全相同且同相，则菱形将移动到显示屏的最右侧。如果它们完全不同，因此没有相位关系，钻石将落在显示屏的中央。

A second feature on the scope in Figure 16.6 shows another useful phase tool. This one helps determine phase with stereo audio that has very different content. The feature is called a Correlation Meter and is represented by a diamond. On the display shown in the figure, there are 5 different Correlation Meters (shown as diamonds), one below each stereo pair of meters, and one below the lissajous display of the signal. The diamond shaped indicator shows how much the channels in the measured stereo pair are similar, or correlate. If they are exactly the same and in-phase, the diamond will move to the far right of the display. If they are completely different, and therefore have no phase relationship, the diamond will fall in the center of the display.

图 16.6（图 23） 同相立体声音频信号

Figure 16.6 (Plate 23) In-Phase Stereo Audio Signal

正确定相的立体声音频会导致菱形在仪表的中心和右侧之间漂移。异相音频会导致菱形开始向中心标记的左侧移动，许多示波器会将菱形变成红色。相位误差越大，钻石将向左移动得越远。

Properly phased stereo audio will cause the diamond to drift between the center and right side of the meter. Out of phase audio will cause the diamond to begin to move to the left of the center mark, and many scopes will turn the diamond red. The greater the phase error, the further to the left the diamond will move.

传输音频

Transporting Audio

在进行大规模视频制作时，有几种常用的方法来管理和移动模拟和数字形式的音频信号。许多从事音乐表演或从事音乐表演工作的人可能熟悉使用双绞线的模拟方法。每个单独的音频信号，如麦克风或乐器，都通过一对绞合在一起的电线传送到混音器和放大器，以减少干扰。通常当有许多信号要四处移动时，比如在舞台接线盒和调音台之间，多组电线会以“mult”形式捆绑在一起。

When working on large scale video productions, there are several common ways to manage and move audio signals both in analog and digital form. Many people, having been in or worked around music performances, may be familiar with the analog method using twisted pair wiring. Each individual audio signal, like microphones or instruments, is carried to mixers and amplifiers on a pair of wires that are twisted together to reduce interference. Often when there are many signals to move around, say between a stage connection box and the mixer, multiple sets of wires are bundled together in “mults.”

随着数字信号的出现，几种其他形式的移动节目的音频部分成为可能。一种选择称为嵌入式音频。在这个系统中，未压缩的音频信号与视频信号和其他元数据一起被插入到数字数据流中。这非常方便，因为单根电缆可以传输多达 16 个通道的数字音频和图片信息。（图 4.1，图 1显示了脉冲交叉显示中的数字音频信号。）

With the advent of digital signals, several other forms of moving the audio portion of the program became possible. One option is called embedded audio. In this system, the uncompressed audio signals are inserted into the digital data stream along with the video signal and other metadata. This is very convenient as a single cable can carry up to 16 channels of digital audio right along with the picture information. (Figure 4.1, Plate 1 shows the digital audio signal in a pulse cross display.)

然而，在大型电视制作中，音频通常由不同的部门和设备处理，直到它被移交给将监督其传输到空气、有线或网络的人员。在这些情况下，使用嵌入在程序视频部分中的音频是低效的或不可能的。

In large TV productions, however, audio is often handled by different departments and equipment right up to the time it is handed off to the people who will oversee its transmission to air, cable or web. In those cases, it is not efficient or possible to work with the audio that is embedded with the video portion of the program.

目前在这些情况下最流行的格式称为 AES，它是信号格式 AES 3 或 AES/EBU 的简写。AES 是音频工程学会，一个对所有音频感兴趣的标准组织。EBU 是欧洲广播联盟，一个处理欧洲广播的标准组织 联盟（您可以在第 12 章阅读更多关于标准的内容）。该标准可追溯到 1985 年，描述了一种以与音频和视频系统需求兼容的方式对数字音频信号进行编码的系统。1985 年，立体声音频是最流行的聆听形式，因此 AES 将其两个通道捆绑在一起成为一个流。因此，AES 的一个“通道”包含两个信号，即一对立体声模拟通道的左右部分（图 16.7）。

Currently the most popular format in these situations is called AES, which is shorthand for the signal format AES 3, or AES/EBU. AES is the Audio Engineering Society, a standards group interested in all things audio. EBU is the European Broadcasting Union, a standards group that deals with broadcasting in the European Union (you can read more on standards in Chapter 12). This standard dates back to 1985 and describes a system of encoding digital audio signals in a way that is compatible with the needs of audio and video systems. In 1985, stereo audio was the most prevalent form of listening, so the AES bundled its two channels together into a single stream. As a result, one “channel” of AES contains two signals, both the left and right portions of a stereo pair of analog channels (Figure 16.7).

图 16.7 AES 数字输入

Figure 16.7 AES Digital Input

AES 旨在与现有的模拟系统一起工作，因此它从一开始就被设计为在双绞线（如模拟音频）或视频信号使用的同轴电缆上传输。这使得转换到数字音频变得容易，因为现有的布线和接线架可以重新用于传输 AES 信号。也可以通过光纤电缆以及消费级电缆和连接来传输信号。

AES was designed to work with the existing analog system, so it was designed from the outset to be carried on either twisted pair wire, like analog audio, or on the kind of coax that video signals use. This made it easy to transition to digital audio as existing wiring and patch bays could be repurposed to carry the AES signal. It is also possible to carry the signal on fiber optic cable, and on consumer grade cable and connections.

AES 并不止于那一种格式。还有另一种格式在大型制作中很常见，称为 AES 10或者更常见的是 MADI（多通道音频数字接口）。顾名思义，这个数字标准旨在承载比 AES 3 立体声对多得多的通道。使用 MADI，可以在一根电缆（铜同轴电缆或光纤）上承载多达 64 个音频通道。这种格式用于连接需要大量音频通道相互连接的设备，例如将工作室路由系统连接到混音器。这也是处理舞台盒想法的一种非常方便的方法。通过在音频信号源附近放置一个 MADI 分线盒，可以将一根同轴电缆或光纤电缆连接回音频混音器。想象一下，将一根电缆从电视转播车铺设到篮球场地板而不是五六根电缆会节省多少时间！

The AES did not stop with just that one format. There is another format that is quite common in large productions known as AES 10 or, more commonly, MADI (Multichannel Audio Digital Interface). As the name implies, this digital standard is designed to carry many more channels than the stereo pair of AES 3. Using MADI, up to 64 channels of audio can be carried on a single cable, either copper coax or fiber optic. This format is used to connect devices that require a lot of audio channels to be connected to each other, such as hooking the studio routing system to the audio mixer. It is also a really handy way to deal with the stage box idea. By putting a MADI breakout box near the source of audio signals, a single coax or fiber cable can be run back to the audio mixer. Imagine the savings in time laying one cable to the floor of the basketball arena from the TV truck instead of five or six mults!

采用减少多通道应用布线的想法并应用计算机网络技术导致另一种有趣的方式来移动音频信号。以太网音频使用计算机网络的标准和惯例对音频信号进行编码。为此有几种不同的专有格式。在撰写本书时，CobraNet 和 Dante 非常流行。

Taking the idea of reduced wiring for multi-channel applications and applying computer networking techniques leads to another interesting way to move audio signals. Audio over Ethernet encodes audio signals using the standards and conventions of computer networking. There are several different proprietary formats for this. As of the writing of this book, CobraNet and Dante were very popular.

使用这些技术，可以通过标准网络布线和分配设备传输数百个单独的音频通道。现在，从大型场所分发和收集音频就像连接网线一样简单。由于大多数电视基础设施正在向基于计算机的技术迁移，这可能会在不久的将来成为音频连接的主要方法。

With these techniques, several hundred individual audio channels may be carried over standard network cabling and distribution equipment. Now distributing and collecting audio from large venues is as simple as connecting a network cable. As most of the infrastructure of television is migrating toward computer based technologies, this will likely become the dominant method for audio connections in the near future.

元数据类型

Types of Metadata

一般而言，元数据信息描述、解释、定位并使检索、使用或管理资源变得更容易。一本书包含信息，但也有关于这本书的信息，例如作者姓名、书名、副标题、出版日期、出版商名称和索书号，以便您知道在图书馆书架上的何处可以找到这本书。图书内容之外的额外信息就是它的元数据。在图书馆系统中记录此信息允许用户通过任何记录的标准搜索书籍，而无需知道书籍内容本身的一个词。

In general, metadata information describes, explains, locates and makes it easier to retrieve, use, or manage a resource. A book contains information, but there is also information about the book, such as the author’s name, book title, subtitle, published date, publisher’s name, and call number so you know where to find the book on a library shelf. This extra information outside of the book content is its metadata. Logging this information in a library system allows a user to search for the book by any of the criteria logged without knowing one word of the book content itself.

DVD 上的电影等媒体也是如此。您无法拿起 DVD 来观看其中的电影，因此您必须在线搜索有关它的信息或阅读 DVD 标签或包装盒。在阅读该信息时，您可能会意识到不同类型的元数据。事实上，存在三种基本类型的元数据：结构型、描述型和管理型。以 DVD 为例，描述性元数据通常包括您可能首先搜索的信息，例如电影标题和主要演员，也许是进一步描述电影的署名（图17.1). 结构元数据包括电影数据的组织方式，例如元数据将包含哪些信息槽。DVD 还将包含管理信息，通常以小字体显示，例如制作它的创作者、工作室或制作公司、制作日期、类型或格式等。

The same is true for media such as a movie on a DVD. You can’t hold up a DVD to see the movie that’s on it, so you have to search for information about it online or read the DVD label or case. While reading that information, you might become aware of the different types of metadata. In fact, there are three basic types of metadata: Structural, Descriptive, and Administrative. Using the DVD as an example, Descriptive metadata often includes the information you might search for first, such as the movie title and main actors, perhaps a byline that further describes the film (Figure 17.1). Structural metadata includes how the movie data is organized, for example what slots of information the metadata will contain. The DVD will also contain Administrative information, often in small print, such as the creator, studio or production company that produced it, the date it was created, perhaps the type, or format, and so on.

图 17.1 元 数据类型

Figure 17.1 Types of Metadata

当您查看此信息时，您很可能永远不会再考虑您正在查看的元数据类型。事实上，类型不如了解元数据的不同使用方式重要。

As you look at this information, it’s quite possible you might never give a second thought to the type of metadata you’re reviewing. In truth, the type is less important than becoming aware of the different ways metadata can be used.

照片中的元数据

Metadata in Photos

您是否看过一张随着年龄增长而开始变黄的旧照片？如果你把照片翻过来，你很可能会看到照片背面写着什么，通常是日期和照片中的人。在元数据被广泛使用之前，这是输入元数据的“人工”或模拟方式。有人写下了他们对这个人、事件或时间的了解。无论采取何种形式，该信息都与照片一起保存。今天，我们做同样的事情，但我们以数字方式进行。使用 Apple 的 iPhoto、Windows Live 照片库和 Picasa 等照片程序，我们可以对照片进行标记和评级、输入标题以及添加关于照片的关键词。这使得组织和检索图像变得非常容易。

Have you ever looked at an old photograph that’s started to yellow with age? If you turned the photo over, it’s very likely you saw something written on its back, usually the date and the person in the photo. Before metadata became widely used, this was the “human” or analog way to enter metadata. Someone wrote down what they knew about the person, event or time. In whatever form it took, that information was kept with the photo. Today, we do the same thing but we do it digitally. Using photo programs such as Apple’s iPhoto, Windows Live Photo Gallery, and Picasa, we are able to label and rate photos, enter captions, and add key words about a photo. This makes it very easy to organize and retrieve images.

虽然人类可以输入关于照片的描述性数据，但还有其他信息，我们称之为结构元数据或管理元数据，拍摄照片的相机知道这些信息。例如，在您拍摄照片时，相机会在图像中嵌入信息，例如文件类型（例如 JPEG、TIFF）、图像分辨率 (3264 × 2448)、拍摄图像的日期和时间，甚至可能是照片的名称相机和文件大小（图 17.2）。此元数据还可以与您自己手动输入的描述信息一起用作搜索条件。

While humans can enter descriptive data about the photos, there is other information, let’s call it structural or sometimes administrative metadata, which the camera that captured the photo knows about the image. For example, the moment you snap a picture, the camera embeds information into the image such as the file type (e.g. JPEG, TIFF), image resolution (3264 × 2448), date and time the image was taken, perhaps even the name of the camera and size of the file (Figure 17.2). This metadata can also be used as search criteria alongside the descriptive information you manually entered yourself.

图 17.2 从 iPhone 导入的图像的 iPhoto 元数据

Figure 17.2 iPhoto Metadata for Image Imported from an iPhone

视频中的元数据

Metadata in Video

与前面的 DVD 电影示例一样，元数据在视频中特别有用，因为它的内容不能直接被计算机破译。由于视频已成为 21 世纪的主要交流和表达形式，因此快速、轻松地组织和访问视频的需求非常重要。视频中使用的第一种元数据形式是时间码。时间码是一种标签系统，提供了一种搜索和编辑单个视频帧的方法。（本章稍后将更详细地讨论时间码。）

Like the DVD movie example sited previously, metadata is particularly useful in video because its contents aren’t directly decipherable by computers. And since video has become a primary form of communication and expression in the 21st Century, the need to organize it and access it quickly and easily is very important. One of the first forms of metadata used in video was timecode. Timecode is a labelling system that provides a way to search and edit individual frames of video. (Timecode is discussed in more detail later in this chapter.)

随着视频数字化，元数据已成为视频数据流的重要组成部分。串行数字视频流中的元数据包含有关正在使用的视频标准、帧速率、行数、音频通道的数量和类型以及使用的压缩和编码系统的信息。允许正确解释数字数据以供使用和显示的任何必要信息都包含在元数据中。不正确的元数据会导致其余数据本身无法使用。不正确的数据标识无法检索。例如，如果元数据指示音频是杜比环绕声，而实际上是双声道立体声，则音频将无法正确再现，因为系统将尝试重新创建不存在的信号。

As video has become digital, metadata has become an essential part of the video data stream. Metadata in the serial digital video stream contains the information about what video standard is being used, the frame rate, line count, the number and type of audio channels, and the compression and encoding system used. Any necessary information to allow the digital data to be correctly interpreted for use and display is contained in the metadata. Incorrect metadata can cause the rest of the data itself to be unusable. Data that is incorrectly identified cannot be retrieved. For example, if the metadata indicates that the audio is Dolby surround sound when it is actually two channel stereo, the audio will not be reproduced correctly as the system will be trying to recreate a signal that is not there.

与静止图像一样，元数据可以通过两种方式附加到视频文件：自动捕获或手动输入。如果它是自动生成和捕获的，则很可能是管理类型的元数据，而手动输入的元数据往往更具描述性。大多数视频元数据是在摄像机中或通过使用软件自动生成的。捕获的信息包含在视频文件中，可以在视频编辑系统中轻松访问（图 17.3）。

As with still images, there are two ways metadata can be attached to a video file: it can be captured automatically or entered manually. If it’s automatically generated and captured, it’s most likely administrative type of metadata, while the manually entered meta-data tends to be more descriptive. Most video metadata is automatically generated in the camera or through the use of software. The information captured is contained within the video file and can easily be accessed in a video editing system (Figure 17.3).

记录素材一直是电影和视频剪辑过程中的一个常规阶段。今天，视频编辑或制作人可以做的不仅仅是命名剪辑。剪辑师可以添加进一步识别剪辑的关键字，例如剪辑中的人物、剪辑的场景、客户是谁，以及旁白或脚本的注释或摘录（图 17.3 ）。一些编辑系统可以识别镜头中的人数以及镜头的类型——广角、中景、特写等等。选择此选项后，将在捕获过程中自动输入信息。越来越多的编辑软件包括元数据条目选项，这些选项增加了您可以添加到视频文件的信息量和种类。

Logging footage has been a customary stage in the editing process, both film and video. Today, the video editor or producer can go way beyond just naming clips. Editors can add keywords that further identify the clip, such as who is in the clip, what scene the clip is from, who the client is, as well as notes or excerpts from the narration or script (Figure 17.3). Some editing systems can recognize the number of people in a shot and what type of shot it is—wide, medium, close-up, and so on. When this option is selected, the information is entered automatically during the capture process. More and more, editing software is including metadata entry options that increase the amount and variety of information you can add to a video file.

图 17.3 Apple 的 Final Cut Pro X 编辑应用程序中的剪辑信息。

Figure 17.3 Clip Information in Apple’s Final Cut Pro X Editing Application.

在此视频剪辑信息窗口中，请注意有些字段是灰色的，有些是黑色的。灰色字段包含已自动输入的摄像机记录数据。这些字段不可编辑。名称、注释、卷轴、场景、镜头等描述性字段是可自定义的字段，您可以在编辑应用程序中手动输入信息。

In this video clip information window, notice that some fields are gray and some are black. The gray fields contain the camera-recorded data, which has been entered automatically. Those fields are not editable. The descriptive fields, such as Name, Notes, Reel, Scene, Take, and so on, are customizable fields where you can enter information manually within the editing application.

广播和网络中的元数据

Metadata in Broadcast and on the Web

如果您是唯一观看您视频的人，并且您知道所有内容在哪里，那么考虑创建结构化元数据系统可能就不那么重要了。但是当视频被广播或上传到互联网时，考虑如何使用元数据是非常重要的。

If you are the only person looking at your video, and you know where everything is, it may be less important to think about creating a structured metadata system. But when video is being broadcast or uploaded to the Internet, it’s very important to think about how the metadata will be used.

例如，全球体育赛事可能由主要广播公司拍摄并存档以备将来播出。但是，如果广播电台的新闻部想要播放获胜达阵的片段怎么办？自动捕获的元数据可能会提供剪辑名称、持续时间、运行时间码和其他信息。但是，如果记录助手在比赛期间发生的位置输入诸如触地得分、伟大的接球或四分卫擒杀等关键字，那么以后想要访问这些信息的编辑和操作员将可以毫不费力地找到他们需要的信息。

For example, a worldwide sports event might be shot by a major broadcaster and archived for future broadcast. But what if the News Department at the broadcast station wanted to air a clip of the winning touchdown? The automatically captured metadata might provide clip names, durations, and running timecode, and other information. But if a logging assistant entered keywords such as touchdown, great catch, or quarterback sack at the locations they occurred during the game, editors and operators who wanted to access that information later would have no trouble finding what they need.

互联网也是如此。网络上的元数据包含网页内容的描述和链接到内容的关键字。此元数据称为元标记，它是 HTML 中的标记或编码语句，用于描述网页内容的某些方面（图 17.4）。该信息可能包括编写网站所用的语言、用于创建网站的工具以及到哪里获取更多信息。某些元标记仅对查找该信息的搜索引擎可见。一些网站，如维基百科，通过要求编辑在文章中添加指向类别名称的超链接，并包括标题、来源和访问日期等引用信息，来鼓励使用元数据。

The same holds true for the Internet. Metadata on the web contains descriptions of the web page contents and keywords that link to the content. This metadata is referred to as metatags, which are tags or coding statements in HTML that describe some aspect of the contents of the Web page (Figure 17.4). That information might include the language the site is written in, the tools used to create it, and where to go for more information. Some metatags are only visible to search engines looking for that information. Some sites, such as Wikipedia, encourage the use of metadata by asking editors to add hyperlinks to category names in the articles, and to include information with citations such as title, source and access date.

图 17.4 网站元标签

Figure 17.4 Website Metatags

元标签和关键字不仅提供了组织和访问媒体的方式，而且还提供了巨大的营销潜力。例如，即使每分钟上传 100 小时的视频（截至撰写本文时），关键字仍可让 YouTube 用户轻松找到特定视频。YouTube 以及其他视频共享网站需要上传视频的元数据，以便每月超过 30 亿的独立用户可以快速找到他们正在寻找的内容并了解有关他们正在观看的视频的更多信息。

Metatags and keywords not only provide ways of organizing and accessing media, but they offer great marketing potential as well. For example, keywords allow YouTube users to easily find specific videos even though 100 hours of video are uploaded every minute (as of this writing). YouTube, along with other video sharing sites, requires metadata for videos being uploaded so the over 3 billion unique users a month can find what they’re looking for quickly and learn more about the video they’re viewing.

时间码元数据

Timecode Metadata

在电视的早期，所有的节目都是现场直播的。存档电视节目的唯一方法是使用称为显像管的过程。Kinescoping 是将 16 毫米电影摄影机聚焦在电视监视器上并拍摄图像的过程。从 20 世纪 50 年代中期开始，当录像带录制被发明时，节目被现场录制，然后在不同的时间播放。这些节目是实时播放的，没有即时重播或冻结帧的好处。当录像带开始用于编辑目的时，识别视频的特定帧、访问这些帧、然后将它们插入并编辑到已编辑母带中的特定位置变得至关重要。传统上可以通过印在胶片上的数字来识别胶片画幅 电影的边缘。与电影不同，在制作时，视频没有可用于识别单个视频帧的编号。

In the early days of television, all programs were broadcast live. The only means of archiving a television program was by using a process called kinescope. Kinescoping was the process of focusing a 16mm motion picture camera at a television monitor and photographing the images. Starting in the mid-1950s, when videotape recording was invented, programs were taped live and then played back for broadcast at a different time. These programs were played in real time without the benefit of instant replays or freeze frames. When videotape began to be used for editing purposes, it became critical to identify specific frames of video, access those frames, then cue and edit them to specific locations in an edited master tape. Film frames traditionally could be identified by numbers imprinted along the edge of the film. Unlike film, at the time of manufacture, video had no numbering that could be used to identify individual video frames.

图 17.5 标记框

Figure 17.5 Labeling Frames

1967 年，视频设备制造公司 EECO 创建了时间码，这是一种可以同步、提示、识别和控制录像带的系统。这种格式被SMPTE（电影电视工程师协会）采纳为标准。SMPTE 时间码在视频的每一帧上记录一个唯一的编号（图 17.5）。使用时间编码视频可确保可以使用相同的时间码号码一次又一次地完全准确地访问特定视频帧。这被称为帧精度，如拥有帧精度编辑系统或进行帧精度编辑。

In 1967, EECO—a video equipment manufacturing company—created timecode, a system by which videotape could be synchronized, cued, identified, and controlled. This format was adopted by SMPTE (the Society of Motion Picture and Television Engineers) as a standard. SMPTE timecode records a unique number on each frame of video (Figure 17.5). Working with timecoded video ensures that a specific video frame can be accessed using the same time-code number over and over again with complete accuracy. This was referred to as frame accuracy, as in having a frame-accurate editing system or making a frame-accurate edit.

读取时间码

Reading Timecode

时间码被读取为数字显示，很像数字时钟。然而，除了数字的小时、分钟和秒时钟，时间码包括帧计数，因此可以识别和访问特定的视频帧。时间码编号显示为冒号分隔每个类别，构造如下：

Timecode is read as a digital display much like a digital clock. However, in addition to the hours, minutes, and seconds of a digital clock, timecode includes a frame count so the specific video frames can be identified and accessed. A timecode number is displayed with a colon separating each category, constructed as follows:

一小时二十分钟三帧的时间码编号将写为 01:20:00:03。第一个数字之前的零不影响数字，并且在编辑系统或其他设备中输入时间码数字时经常被省略。但是，数字后面的分、秒和帧类别必须使用零，因为它们包含特定的位值。

A timecode number of one hour, twenty minutes, and three frames would be written as 01:20:00:03. The zeros preceding the first digit do not affect the number and are often omitted when entering time-code numbers in editing systems or other equipment. However, the minutes, seconds, and frames categories following a number must use zeros, as they hold specific place values.

以下是如何读取和标记时间码的一些示例：

Here are some examples of how timecode is read and notated:

时间码使用军用时钟时间，从 00:00:00:00 到 23:59:59:29，即从午夜到午夜前的帧。在 30 fps 标准中，如果将一帧添加到最后一个数字，该数字将再次变为全零，即午夜。30 fps 视频的帧数由 00 到 29 之间的 30 个数字表示。数字 29 将是该系统中帧的最高值。将一帧添加到 29，帧数变为零，而秒数增加 1。24 fps 视频的帧数由 00 到 23 之间的 24 个数字表示。

Timecode uses military clock time in that it runs from 00:00:00:00 to 23:59:59:29, that is, from midnight to the frame before midnight. In a 30 fps standard, if one frame is added to this last number, the number turns over to all zeros again, or midnight. The frame count of a 30 fps video is represented by the 30 numbers between 00 and 29. The number 29 would be the highest value of frames in that system. Add one frame to 29, and the frame count goes to zeros while the seconds increase by 1. The frame count of a 24 fps video is represented by the 24 numbers between 00 and 23.

时间码可用于任何可用的视频标准，而不管该标准的帧速率如何。时间码编号过程中的唯一区别是指示帧的最后两位数字可能出现不同。帧将反映选择作为记录格式的任何帧速率。例如，24 fps HDTV 标准中的时间码位置可能是 1:03:24:23，代表那一秒的最后一帧；而 30 fps HDTV 标准的最后一帧是 1:03:24:29。

Timecode can be used with any available video standard regardless of that standard’s frame rate. The only difference in the timecode numbering process is that the last two digits indicating frames may appear differently. The frames will reflect whatever frame rate was chosen as the recording format. For example, a timecode location in a 24 fps HDTV standard might be 1:03:24:23, which represents the last frame of that second; whereas the last frame of a 30 fps HDTV standard would be 1:03:24:29.

时间码格式

Timecode Formats

自开发以来，时间码有多种格式。原始格式是纵向或线性时间码，或LTC。纵向时间码是记录为音频信号的数字信号。

Since its development, timecode has had several formats. The original format was Longitudinal or Linear Timecode, or LTC. Longitudinal timecode is a digital signal recorded as an audio signal.

另一种时间码格式是Vertical Interval Timecode或VITC，读作vit-see。LTC 是音频信号，而 VITC 作为模拟视频信号的一部分记录为垂直间隔中的视觉数字信息。VITC 必须与视频同时录制。记录后，VITC 可用于识别静止模式或运动中的视频帧。

Another timecode format is Vertical Interval Timecode, or VITC, pronounced vit-see. While LTC is an audio signal, VITC is recorded as visual digital information in the vertical interval as part of the analog video signal. VITC must be recorded simultaneously with the video. Once recorded, VITC can be used to identify a frame of video either in still mode or in motion.

在数字记录格式中，时间码作为元数据的一部分包含在数字流或文件结构中。在 SDI 和 HDSDI 等数字视频信号中，这是HANC（水平辅助数据）。对于 MXF 和 QuickTime 等基于文件的录制，时间码被编码在为此目的保留的虚拟轨道上。

In digital recording formats, the timecode is carried as part of the Metadata contained within the digital stream or file structure. In digital video signals such as SDI and HDSDI, this is part of the HANC (Horizontal Ancillary Data). For file-based recording such as MXF and QuickTime, the timecode is encoded on a virtual track reserved for this purpose.

非丢帧和丢帧时间码

Non-Drop-Frame and Drop-Frame Timecode

创建时间码时，NTSC 视频以每秒 29.97 帧的速度运行。这是允许彩色广播的技术改编。换句话说，扫描完整的 30 帧需要超过 1 秒的时间。事实上，扫描 30 帧彩色视频需要 1.03 秒。

When timecode was created, NTSC video ran at 29.97 frames per second. This was a technical adaptation to allow color broadcasts. In other words, it takes more than 1 second to scan a full 30 frames. In fact, it takes 1.03 seconds to scan 30 frames of color video.

时间码必须考虑到这个微小的差异。如果每个视频帧都使用 30 fps 时间码按顺序编号，则在一个小时结束时，时间码将显示为 59 分 56 秒 12 帧，或者少了 3 秒 18 帧，即使程序运行了一个完整的小时。每秒的帧数更少，因此一小时内的帧数更少。

Timecode had to account for this small difference. If every video frame was numbered sequentially with 30 fps timecode, at the end of an hour the timecode would read 59 minutes, 56 seconds, and 12 frames, or 3 seconds and 18 frames short of an hour, even though the program ran a full hour. There are fewer frames per second and thus fewer frames in an hour.

广播节目必须有准确的时间长度，以保持通用的时间表。为了让时间码可以作为时钟时间的参考，SMPTE规定了一种弥补3秒18帧或108帧差异的时间编码方法。确定应该通过定期推进时钟来从连续代码中删除数字。通过这样做，在一个小时的时间结束时，时间码数字将有一个小时的持续时间。

Broadcast programs have to be an exact length of time in order to maintain a universal schedule. In order to allow timecode to be used as a reference to clock time, SMPTE specified a method of timecoding that made up for the 3 seconds and 18 frames, or a 108-frame difference. It was determined that numbers should be dropped from the continuous code by advancing the clock at regular intervals. By doing this, there would be an hour’s duration in timecode numbers at the end of an hour’s worth of time.

该公式开始时每分钟将时钟推进两帧时间码数字，每十分钟除外（10、20、30 等）。通过每分钟前进 2 帧，将丢弃总共 120 帧，或比所需的 108 帧多 12 帧。但是除了几十分钟以外，每分钟掉2帧将是 54 分钟 × 2 帧/分钟，等于 108 帧，占识别真实时钟时间段所需的帧数。SMPTE参照其过程将新的时间编码替代方法命名为彩色视频丢帧时间码。丢帧时间码有时称为一天中的时间或 TOD 时间码。最初的 30 fps 连续代码后来被称为非丢帧时间码（图 17.6）。

The formula began by advancing the clock by two frames of time-code numbers each minute, except every tenth minute (10, 20, 30, and so on). By advancing 2 frames on every minute, a total of 120 frames, or 12 more than the 108 frames needed, would be dropped. But 2 frames dropped from every minute except the tens of minutes would be 54 minutes × 2 frames per minute, which equals 108 frames, accounting for the necessary number of frames to identify a true clock time period. SMPTE named the new alternative method of time coding color video drop-frame timecode in reference to its process. Drop-frame timecode is sometimes referred to as time of day, or TOD timecode. The original 30 fps continuous code was subsequently termed non-drop-frame timecode (Figure 17.6).

在丢帧时间码中，时间码总是通过跳过每分钟的前两个帧号来提前，每隔十分钟除外。例如，编号顺序将从一帧的 1:06:59:29 到下一帧的 1:07:00:02（见图17.6）。跳过的两个帧编号是 1:07:00:00 和 1:07:00:01。在第十分钟，没有数字被跳过。例如，每十分钟的编号顺序将从一帧的 1:29:59:29 到下一帧的 1:30:00:00。

In drop-frame timecode, the timecode is always advanced by skipping the first two frame numbers of each minute except every tenth minute. For example, the numbering sequence would go from 1:06:59:29 on one frame to 1:07:00:02 on the very next frame (see Figure 17.6). The two frame numbers that are skipped are 1:07:00:00 and 1:07:00:01. At the tenth minute, no numbers are skipped. The numbering sequence at each tenth minute would go from, for example, 1:29:59:29 on one frame to 1:30:00:00 on the next.

图 17.6 时间码格式

Figure 17.6 Timecode Formats

与非丢帧时间码一样，丢帧时间码不会留下任何未标记的视频帧，也不会删除任何帧的图片信息。跳过的数字不会打乱某些编辑系统读取和提示时间码所需的升序。但是在一个小时的素材结束时，时间码数字中将反映一个小时的持续时间。

Like non-drop-frame timecode, drop-frame timecode leaves no frames of video unlabeled, and no frames of picture information are deleted. The numbers that are skipped do not upset the ascending order that is necessary for some editing systems to read and cue to the timecode. But at the end of an hour’s worth of material, there will be an hour’s duration reflected in the timecode number.

每秒 24 帧的时间码

Timecode at 24 Frames Per Second

虽然使用术语 24 fps 和 30 fps 是为了方便起见，但大多数系统使用的真实帧速率分别为 23.976 fps 和 29.97 fps。视频的 SMPTE 时间码以与视频相同的帧速率运行，在丢帧时间码模式下为 29.97 fps。24 fps 视频系统中使用的时间码以 23.976 fps（也称为 23.98）运行。在 24 fps 系统中没有丢帧或非丢帧模式，因为没有像 NTSC 开发的原始视频系统那样冲突的单色与彩色帧率。由于决定了单个帧速率并且同步是固定的，因此开发了时间码系统以保持时钟准确时间。如果最初的 NTSC 系统是从彩色开始的，那么同时开发的时间码系统将不再需要一种以上的时间码。

While the terms 24 fps and 30 fps are used for convenience, the true frame rates that most systems use are 23.976 fps and 29.97 fps respectively. SMPTE timecode for video runs at the same frame rate the video does, 29.97 fps in drop-frame timecode mode. Timecode used in the 24 fps video system runs at 23.976 fps, also referred to as 23.98. There are no drop-frame or non-drop-frame modes in a 24 fps system because there are no conflicting monochrome versus color frames rates as there were in the original video systems developed by the NTSC. As a single frame rate is decided upon and the synchronization is fixed, a timecode system is developed to keep clock accurate time. Had the original NTSC system started with color, the timecode system developed simultaneously would have eliminated the need for more than one type of timecode.

为了简化 24 fps 到 30 fps 的转换，必须将帧速率从 24 fps 更改为 23.98 fps。没有它，将真正的 24 fps 图像和时间码转换为视频中现有的 29.97 帧速率会复杂得多。将 24 fps 电影或 HD 转换为 30 fps 视频时，会在添加额外帧时添加额外时间码编号。当以另一种方式从 30 fps 传输到 24 fps 时，附加数字将被删除，并且时间码会随着附加场和帧被删除而重新排序。

This alteration in the frame rate from 24 fps to 23.98 fps was necessary to simplify the 24 fps to 30 fps conversion. Without it, converting true 24 fps images and timecode to the existing 29.97 frame rate in video would be much more complex. When converting 24 fps film or HD to 30 fps video, the additional time-code numbers are added as the additional frames are added. When transferring the other way, from 30 fps to 24 fps, the additional numbers are deleted and the timecode is resequenced as the additional fields and frames are deleted.

视觉时间码

Visual Timecode

图 17.7 可视时间码

Figure 17.7 Visual Timecode

时间码也可以显示为视觉图像上的数字。这是通过使用字符或文本生成器或有时通过编辑系统中的内部过滤器来实现的。这 时间码信号被送入字符发生器，字符发生器依次显示时间码数字的视觉翻译。该显示位于视频素材之上，可以显示在监视器上或记录到图片中（图 17.7）。视觉时间码不是机器、计算机或时间码阅读器可以读取的信号。

Timecode can also be displayed as numbers over the visual images. This is achieved through the use of a character or text generator or sometimes through an internal filter in an editing system. The timecode signal is fed into the character generator, and the character generator in turn displays a visual translation of the timecode numbers. That display is placed over the video material and can be shown on the monitor or recorded into the picture (Figure 17.7). Visual timecode is not a signal that can be read by machine, computer, or timecode reader.

大规模工作流程

Large-Scale Workflows

想象那个创造性灵魂单独工作的工作流程可能相对容易。那个富有创造力的灵魂甚至可能就是你。但是为了完全理解大规模工作流的一些需求和可能性，想象一个假想的可能会有所帮助 电视网。图 18.1中的图表显示了一个大规模工作流的通用示例，可​​用于检查每个元素并查看它们之间的关系。

It might be relatively easy to imagine the workflow of that creative soul working alone. That creative soul might even be you. But in order to fully understand some of the needs and possibilities of a large-scale workflow, it might be helpful to think of an imaginary television network. The diagram in Figure 18.1 shows a generic example of a large-scale workflow that can be used to examine each of the elements and see how they relate.

图 18.1 大规模工作流

Figure 18.1 Large-Scale Workflow

中央存储

Central Storage

工作流的中间是文件实际存储的地方。在图中，这称为中央存储。实际上，大型企业很少有单一的材料存储库。更有可能的是，存在一组地理上不同的存储集群，其中包含材料的副本。这有助于使媒体文件可供不同地区的人们使用。更重要的是，它提供了多个位置以防灾难发生其中一个站点离线。进行像世界杯这样的大型国际制作的广播公司可能在主办国有一个存储集群，并将内容镜像到他们本国基地的另一个集群。两国的内容创作者都可以访问他们所需材料的本地副本。如果一个位置发生系统故障，内容在另一个位置仍然完好无损。

In the middle of the workflow is the place that the files are actually stored. In the diagram, this is called Central Storage. In reality, large enterprises seldom have a single repository for their material. More likely, there is a geographically diverse group of storage clusters that contain duplicates of the material. This serves to make the media files available to people in different regions. More importantly, it provides multiple locations in case a disaster takes one of the sites offline. A broadcaster doing a large international production like the World Cup might have a storage cluster in the host country, and mirror the content to another cluster at their home base. Content creators in both countries can access local copies of the material they need. If a system failure occurred in one location, the content would still be in tact at the other.

档案

Archive

中央存储用于及时或经常需要的文件。但是，存档是当前未使用但必须保存的文件所在的位置。大多数情况下，这包括一个自动磁带库。当大规模完成时，这是一组由机器人维护的磁带，可以机械地从播放器上加载和卸载。在存储大型数据集时，磁带比旋转磁盘驱动器更便宜且更可靠。缺点是不能即时访问。必须找到带有请求文件的磁带并将其加载到播放器中，然后必须将文件复制到中央存储器以供访问。

Central Storage is used for files that are needed either in a timely fashion or on a frequent basis. The archive, however, is where files that are not currently being used, but must be saved, are located. Most often this consists of an automated tape library. When done on a large scale, this is a robotically maintained set of tapes that can be loaded and unloaded from players mechanically. Tape is both less expensive and more robust than spinning disk drives when storing large data sets. The drawback is that it cannot be accessed instantly. The tape with the requested file must be located and loaded into a player and then the file has to be copied to central storage for access.

摄入和质量控制

Ingest and Quality Control

实际将材料放入中央存储系统的工作落在了 Ingest 操作员身上。提要可能来自本地工作室或摄像机，通过微波、卫星或光纤线路的远程提要，甚至作为内容贡献者在局或现场上传的文件。Ingest 操作员负责在材料移入中央存储时对其进行管理。

The job of actually getting material into the Central Storage system falls to Ingest operators. Feeds may come from local studios or cameras, remote feeds via microwave, satellite or fiber optic lines, or even as files uploaded by content contributors at bureaus or in the field. The Ingest operators are responsible for managing the material as it is moved into Central Storage.

材料入库后，必须在质量检查期间检查某些程序和材料的质量控制过程，有时简称为 QC。这可以通过两种方式完成。一种方法是让材料通过自动化质量控制系统。另一种方法是让质量控制操作员执行手动检查。不管怎么做，重要的是必须保持节目素材的技术标准和内容标准。

Once the material has been ingested into storage, some programs and materials must be examined for quality during a Quality Control process, sometimes referred to simply as QC. This can be done in two ways. One way is to pass the material through an automated Quality Control system. The other way is to have a Quality Control operator perform a manual inspection. However it’s done, it is important that both technical standards and content standards of program material must be maintained.

后期制作

Post Production

有些节目是现场直播的，例如新闻广播或体育赛事直播。但通常情况下，节目需要经过后期制作过程，在后期制作过程中可以操纵和处理内容以为观众准备节目。（后期制作是本书范围之外的一个大话题。） 电视台和网络使用的大部分内容都是在网络系统之外创建的，经过编辑后作为成品引入。但是，某些材料可能仍需要结合内部演出进行编辑。根据网络的不同，邮政部门可能规模不大，也可能规模庞大。像电影频道这样的东西可能只有几个后期制作席位用于宣传或修复，而新闻或体育网络可能有几层楼的编辑室来准备故事、精彩片段、宣传片和其他节目材料。

Some shows are broadcast live, such as newscasts or live sports events. But typically, a show needs to go through the post production process, where content can be manipulated and processed to prepare the show for its audience. (Post production is a huge topic outside the scope of this book.) Much of the content used by TV stations and networks is created outside the network system and brought in after it has been edited as a finished work. However, some materials may still need to be edited in association with in-house shows. Depending on the network, the post department may be modest or enormous. Something like a movie channel might have only a few seats of post production used for promotional spots or fixes, while a news or sports network might have several floors of edit rooms preparing stories, highlights, promos and other show materials.

无论数量如何，后期制作编辑间都与中央存储接口，作为工作素材来源和返回完成剪辑的地方。

Regardless of number, the post production editing bays all interface to Central Storage as both a source of material to work with and a place to return finished clips.

播出和交付

Playout and Delivery

电视网络甚至地方台都不是单一频道。一些有线网络设施支持多个频道的内容同时提供给他们的观众。在此外，每个频道可能有多个不同时区的信息。这些延迟的提要可能有不同的商业广告，以及针对区域观众量身定制的广告。西海岸的人们可能会看到 Best Foods 品牌的蛋黄酱广告，而东海岸则在同一地点看到 Hellmann's，这是一个地区性名称。

Television networks and even local stations are not single channels. Some cable network facilities support many channels of content being made available to their audiences simultaneously. In addition, each of the channels may have multiple feeds to different time zones. Those delayed feeds might have different commercial breaks with spots tailored to regional audiences. Folks on the West Coast may be seeing a mayonnaise commercial for Best Foods brands, while the East Coast is enjoying the same spot but for Hellmann’s, which is a regional name.

管理这些细节是播出功能。为每个频道准备了自动的节目和广告时间表，这些频道会根据正确的路径提示和播放素材。播出部门通常由控制室组成，操作员使用专用设备。视频服务器、自动化系统和调度软件等设备与视频切换器、混音器和路由器集成在一起（图 18.2（图 24））。对于传统的广播操作，这是为制作内容所付出的所有努力的产物最终交付给观众的地方。在商业电台中，这也是插入广告的地方，即支付账单的方式。

Managing these details is the Playout function. Automated schedules of programs and commercials are prepared for each channel, which cue and play the material to the correct path. Playout Departments often consist of control rooms with operators using specialized equipment. Devices such as Video Servers, automation systems and scheduling software are integrated with video switchers, audio mixers and routers (Figure 18.2 (Plate 24)). For a traditional broadcast operation, this is where the product of all the efforts put into producing the content is finally delivered to the viewer. In a commercial station this is also where the advertising, which is how the bills get paid, is inserted.

访问中央存储的另一种方式是视频点播 (VOD)。许多内容频道根据要求将他们的一些材料作为单独播放提供给观众。视频点播和流媒体的主题将在第 21 章中进一步讨论。

Another way to access the Central Storage is Video on Demand (VOD). Many content channels make some of their material available to the audience as individual play outs by request. The topic of Video on Demand and Streaming Media is discussed further in Chapter 21.

审查和筛选

Review and Screening

在我们制作的网络中，有很多人需要在制作和后期制作过程中的不同时间筛选和审查节目和商业内容。例如，制作人可能需要在新闻报道播出前签字。但制片人没有必要在其作品中看到这个故事

Throughout our made-up network, there are many people who will need to screen and review program and commercial content at different times during the production and post production process. For example, a producer may need to sign off on a news story before it airs. But it’s not necessary for the producer to see the story in its

图 18.2（图 24） 自动播出系统（XeusMedia Technology）图 18.2（图 24）

Figure 18.2 (Plate 24) Automated Playout System (XeusMedia Technology) Figure 18.2 (Plate 24)

最高质量的形式。体育记者可能需要查看使用他的剧本编辑过的作品，但他或她正在现场使用笔记本电脑。为此，办公室计算机网络通常会链接到中央存储，让人们可以在办公桌前或远程轻松查看或筛选文件。

highest quality form. A sports writer may need to view an edited piece that used his script, but he or she is on location using a laptop. To that end there is often a link to Central Storage from the office computer network to allow people to simply view or screen files at their desks or remotely.

转码

Transcoding

媒体文件有许多不同的形式。这些具有使它们非常适合一种用途但难以用于另一种用途的属性。转码功能在不同的编解码器和容器中复制材料，使设施的每个区域都可以根据自己的要求发挥作用。

Media files come in many different forms. These have attributes that make them ideal for one purpose, but difficult to use for another. The transcoding function makes duplicates of the material in different codecs and containers that allow each area of the facility to function based on its own requirements.

例如，用于播出的高质量文件太大而无法通过办公室网络传输以供审阅。转码功能可用于制作较小的副本或代理副本以供审阅之用。并且通过 Internet 播出的节目也需要采用不同于原始高质量文件的格式。（在下一章中，您将仔细研究转码、编解码器、包装器和文件类型完成此工作流程。）

For example, the high quality files used for playout are far too large to travel through an office network for review. The transcoding function could be used to make a smaller, or proxy, copy for review purposes. And shows that will air via the Internet would also need to be a different format than the original high quality file it originated in. (In the next chapter, you will take a closer look at transcoding, codecs, wrappers and the types of files that move through this workflow.)

媒体资产管理

Media Asset Management

在大型设施中，存储和访问的文件数量很快就会变得不堪重负。帮助组织媒体是资产管理部门的工作。资产管理是一类对存储的材料进行分类的程序。目录功能允许用户对剪辑数据库进行分类和搜索以查找特定材料。这很像进行 YouTube 搜索以过滤数千万个剪辑以找到您要查找的剪辑。

In a large facility, the number of files stored and accessed can quickly become overwhelming. It is the job of Asset Management to help organize the media. Asset Management is a class of programs that catalog the stored material. The catalog function allows users to sort and search the database of clips for specific material. This works much like doing a YouTube search to filter down tens of millions of clips to find the one you’re looking for.

正如上一章所讨论的，有关文件或元数据的信息可能部分来自文件本身。工作人员，有时称为媒体经理，可以手动输入或记录有关媒体资产的其他详细信息。元数据中的丰富细节大大增强了以后对材料的搜索。

As discussed in the previous chapter, the information about the files, or metadata, may come in part from the file itself. Workers, sometimes called Media Managers, may enter or log additional detail manually about the media assets. Later searches for material are greatly enhanced by rich detail in the metadata.

资产管理也可以帮助处理和指导文件。例如，根据一组访问频率和日期的规则，程序可能会自动将文件移交到档案库进行存储。它还可能负责自动化转码过程，再次基于一组关于哪些文件必须以何种格式可用的规则。

Asset management may also help process and direct the files. For example, based on a set of rules for the frequency and date of access, the program might automatically hand a file off to the archive for storage. It might also be responsible for automating the transcoding process, again based on a set of rules about what files must be available in what formats.

计算机网络和存储

Computer Networking and Storage

为了在视频操作中使用的计算机之间共享媒体文件，它们必须能够通过计算机网络传输。您已经学习了大规模工作流的组件。让我们深入了解此操作并了解计算机如何通信以使此工作流程成为可能以及材料如何存储。

In order to share media files among the computers used in a video operation, they must be capable of being transferred over computer networks. You’ve learned the components of a large-scale workflow. Let’s go under the hood of this operation and learn how the computers communicate in order to make this workflow possible and also how the material is stored.

通过 Internet 协议进行通信

Communicating Via Internet Protocol

让我们考虑一个简单网络的示例，其中有六台计算机通过集线器相互连接。任何网络中的每台计算机都必须有一个唯一的地址。大多数人都熟悉 Internet 协议格式或 IP 地址。目前使用的一个IP版本是IPv4（Internet Protocol version 4），它使用一个32位的数字：四组数字，一组一到三个数字，每组用句点分隔。IP 地址的一个示例可能是 192.16.213.254。

Let’s consider an example of a simple network that has six computers connected to each other through a hub. Each computer in any network must have a unique address. Most are familiar with the Internet Protocol format, or IP address. An IP version in current use is IPv4 (Internet Protocol version 4), which uses a 32-bit number: four sets of numbers, one to three numbers in a set, each set separated by a period. One example of an IP address might be 192.16.213.254.

IP 地址可由用户或系统管理员设置。在某些系统设计中，每台计算机都被赋予一个固定地址，以便其他系统立即知道将数据发送到哪里。然而，更常见的情况是，计算机所连接的路由器或服务器会在一定时间内分配 IP 地址。这种技术称为动态主机配置协议或 DHCP，很可能是您的家庭系统的设置方式（图 18.3）。

An IP address can be set by users or system administrators. In some system designs, each computer is given a fixed address so other systems know immediately where to send data. More frequently, however, a router or server—that the computer is connected to—assigns the IP address for a certain amount of time. This technique is known as Dynamic Host Configuration Protocol, or DHCP, and is most likely how your home system is set up (Figure 18.3).

图 18.3 DHCP 服务器流程

Figure 18.3 DHCP Server Flow

当我们示例中的一号计算机要将文件发送到三号计算机时，它首先将内容分成称为数据包的小包。组成文件的每个数据包都有一个标识号，以便接收计算机知道它在最终文件中的位置。数据包还获得了目标计算机的 IP 地址，在我们的例子中是第三个，以及发送计算机的返回地址。

When computer number one in our example wants to send a file to computer number three, it first breaks the content into small bundles called packets. Each packet that makes up the file gets an identification number so that the receiving computer knows where it fits in the final file. The packets also get the IP address of the destination computer, number three in our case, as well as the return address of the sending computer.

发送计算机接收第一个数据包并将其发送到集线器。集线器然后将其发送到所有其他计算机。每个都查看数据包的地址，如果不是预期的接收者则忽略数据。作为预期目标的计算机，在本例中为三号，将数据包存储在计算机的内存中，并将收据作为消息发送回发件人一号。然后发送方从文件中发送下一个数据包。

The sending computer takes the first packet and sends it toward the hub. The hub then sends it out to all other computers. Each looks at the address of the packet, and ignores the data if not the intended recipient. The computer that is the intended target, in this case number three, stores the packet in the computer’s memory and sends a receipt as a message back to the sender, number one. The sender then sends the next packet in from the file.

在两台计算机要同时发送数据包之前，所有这一切都运行良好。如果一台计算机当前正在发送数据包而另一台计算机开始传输，则数据包会发生冲突。这会破坏数据并且传输失败。两台计算机等待一段随机的时间，然后再次发送它们的数据包。

All this works well until two computers want to send a packet at the same time. If one computer is currently sending a packet and a second computer starts to transmit, the packets collide. This corrupts the data and the transmission fails. Both computers wait a random amount of time and send their packets again.

此设计专为非实时传输而构建。然而，在我们的音频和视频世界中，一个繁忙的网络和许多冲突意味着接收计算机很可能在下一个数据包到达之前用完所有材料来播放。

This design was built for non-real time transfer. However in our world of audio and video, a busy network with many collisions means that the receiving computer may well run out of material to play before the next packet arrives.

在这个简单的示例中，集线器是我们网络的中心。集线器是一项较旧的技术，主要被称为交换机和路由器的设备所取代。这些更高级的设备不会同时将数据包发送到所有其他计算机。相反，它们具有检查数据包并仅将它们发送到目标计算机的智能。此外，这些设备中的一些更复杂的设备将缓冲传入的数据包，并在线路可用时将它们发送出去——从而大大减少了冲突。

In this simple example, a hub was the center of our network. Hubs are an older technology, largely replaced by devices called switches and routers. These more advanced devices do not send the packets to all the other computers at the same time. Rather they have the intelligence to examine the packets and only send them to the destination computer. Additionally some of the more sophisticated of these devices will buffer incoming packets and send them out when the lines are available—greatly reducing the collisions.

全球网络

Global Networking

到目前为止，我们的模型是几台彼此靠近的计算机。这称为局域网或 LAN。然而，现实世界中的网络——例如 Internet 和由公司运营的大型专用网络——是全球性的，并且连接着数百万台计算机。在这个广域网（或 WAN）环境中，两台想要交换文件的计算机可能没有连接到同一个交换机或路由器（图 18.4）。他们甚至可能不在同一个大陆上。

So far our model is of a handful of computers located close to each other. This is referred to as a Local Area Network, or LAN. However, real world networks—such as the Internet and large-scale private networks like those operated by corporations—are global and connect many millions of computers. In this Wide Area Network (or WAN) environment, two computers that want to exchange files may not be connected to the same switch or router (Figure 18.4). They may not even be on the same continent.

当数据包从一台计算机传送到另一台计算机时，数据包通常会通过许多跃点从一个路由器传递到另一个路由器。对于音频和视频等大文件，在传输过程中，随着网络流量的变化，一些数据包可能会采用不同的路由。发生这种情况时，数据包可能会到达秩序。大多数文件播放器会在文件开始播放之前缓冲一些数据包，以帮助解决这个问题。

Often packets of data are passed from router to router through many hops as they make their way from one computer to another. With large files such as audio and video over the course of the transmission, some packets may take different routes as traffic on the network changes. When this happens, packets may arrive out of order. Most file players will buffer a number of packets before a file begins to play to help deal with this problem.

图 18.4 连接到广域网的局域网

Figure 18.4 Local Area Networks Connected to a Wide Area Network

除了流量方面的考虑，我们的网络还必须足够快以传输音频和视频文件中包含的数据量。文档不包含真正大量的数据。这本书不到 100 兆字节。一个典型的办公网络可以在大约八秒内移动那么多的数据。这很好，但压缩到同样 100 兆字节大小的高质量媒体文件只有大约三秒长。那意味着你如果不反复停顿，就无法在网络上实时观看该文件。

In addition to traffic considerations, our networks have to be fast enough to move the amount of data contained in audio and video files. Documents do not contain really huge amounts of data. This book is less than 100 megabytes. A typical office network could move that amount of data in about eight seconds. That is great but a high quality media file compressed to that same 100 megabyte size is only about three seconds long. That means you cannot watch that file in real time on the network without it stalling repeatedly.

此处描述的办公室网络以每秒 100 兆位的速率移动数据。在典型的办公条件下，这是一个古老而普遍的标准。对于媒体应用程序，以更快 10 倍、每秒 1,000 兆位或称为 GigE 的标准连接计算机要普遍得多。GigE 速度很容易在 LAN 类型的设施中实现，在这种设施中，所有计算机都可以连接到本地交换机和路由器。要在远距离的广域网（或 WAN）中实现这种速度，必须以比典型的家庭或小型办公室连接高得多的成本与网络带宽提供商进行特殊规定。

The office network described here moves data at a rate of 100 megabits per second. That is an older and common standard in typical office conditions. For media applications, it is far more common to connect computers at a standard that is 10 times faster, 1,000 megabits per second, or GigE as it is called. GigE speeds are easy to achieve in a LAN-type of facility where all the computers can be connected to local switches and routers. To achieve that kind of speed in a Wide Area Network (or WAN) over long distances, special provisions must be made with network bandwidth providers at a much higher cost than a typical home or small office connection.

速度的下一个重大飞跃是所谓的 10GigE。这比 GigE 连接快十倍。这最常通过光纤电缆传输，因为很难通过普通铜线快速传输信号。这些类型的连接通常在承载设施周围流量的交换机和路由器之间建立。但是，可以将这些超高速连接提供给需要比 GigE 连接提供的数据速度更快的数据速度的计算机。处理大型 RAW 类型数据文件的工作站可能需要这种级别的连接才能全速访问它正在处理的数据。

The next big leap in speed is to something called 10GigE. This is ten times faster than the GigE connection. This is most frequently carried on fiber optic cable, as it is difficult to move signal over normal copper wire that quickly. These types of connections are usually made between switches and routers that carry traffic around a facility. It is possible, however, to give these superfast connections to computers that need more data speed than that offered by GigE connections. A workstation that is working with large RAW type data files may need this level of connection to get to the data it is manipulating at full speed.

也可以从公共带宽提供商那里租用这种速度的连接。当广播公司进行超级碗或四强大学篮球报道等大型远程赛事时，他们可能会租用这些超高速连接。不仅是比赛的节目源，还有回复服务器和编辑系统上的个别剪辑都可以在工作室和活动之间共享。

It is also possible to lease connections of this speed from public bandwidth providers. When broadcasters are doing large remote events like the Super Bowl or Final Four college basketball coverage, they may lease these superfast connections. Not only the program feed of the game, but also individual clips on reply servers and edit systems can then be shared between studio and event.

数据存储

Data Storage

在第 20 章中，您将学习如何将数据记录到硬盘驱动器和磁盘驱动器上的机制，以及如何将驱动器组合在一起以创建存储集群的一些注意事项。在深入了解媒体如何记录到驱动器之前，让我们更广泛地了解一下不同的存储设备以及它们连接到计算机的方式。

In Chapter 20 you will learn the mechanics of how data is recorded onto hard drives and disk drives, and some considerations for how to group drives together to create storage clusters. Before you take that deep dive into how media is recorded onto drives, let’s take a broader look at the different storage devices and the ways they can connect to computers.

直连存储

Direct Attached Storage

直接附加存储是直接连接到负责存储文件的计算机的一类设备。这种形式的某些形式存在于计算机本身内部，如旋转硬盘或固态存储设备 (SSD)。其他的，例如 USB（通用串行总线）或 Thunderbolt 硬盘驱动器，安装在外壳中并通过电缆连接到计算机。

Direct attached storage is the class of devices that are connected directly to the computer that is responsible for storing files. Some forms of this are internal to the computer itself, either as a spinning hard disk or a Solid-State Storage Device (SSD). Others, such as a USB (Universal Serial Bus) or Thunderbolt hard drive, are mounted in external cases and connect to the computer through a cable.

虽然内置驱动器可以轻松地记录和播放媒体文件，但它们的容量有限，因为它们的数量很少，只能放入计算机机箱中。有几种不同的方式可以将它们连接到计算机。目前常见的形式有SATA（Serial Advanced Technology Attachment）和SAS（Serial Attached SCSI）。这些技术都建立在旧标准 PATA 和 SCSI 的基础上，但工作速度更快，布线方案也更简单。这两种接口都可以高速传输数据，目前约为每秒 6 吉比特。这足以处理未压缩的高清视频文件。

While internal drives can easily record and play back media files, they are somewhat limited in capacity, based on the small number of them that fit in a computer case. There are several different ways these may be interfaced to the computer. Current common forms are SATA (Serial Advanced Technology Attachment) and SAS (Serial Attached SCSI). These technologies both build on older standards, PATA and SCSI, but work faster and with less complex wiring schemes. Both of these interfaces can move data at high speed, currently about 6 gigabits per second. That is enough bandwidth to handle even uncompressed high definition video files.

然而，磁盘驱动器是使用高速旋转部件的机械设备，并​​且经常发生故障。在这些高比特率下，将数据传入和传出硬盘的接口可以超过驱动器本身可以读取和写入数据的速率。通过将驱动器组合在一起，可以在多个磁盘上复制数据。这种冗余称为RAID系统，独立磁盘冗余阵列。RAID 系统的优势之一（将在第 20 章中更详细地讨论）是通过将磁盘组合在一起并将数据分布在驱动器上，性能可以比任何单个驱动器都要好。

However, disk drives are mechanical devices using high speed spinning components, and frequently fail. And at these high bit rates, the interface to get the data to and from a hard drive can exceed the rate that the drive itself can read and write the data. By grouping drives together, data can be duplicated on more than one disk. This type of redundancy is referred to as a RAID system, a Redundant Array of Independent Disks. One of the advantages of RAID systems (which are discussed in more detail in Chapter 20) is that by ganging disks together and spreading the data across the drives, performance can be greater than any individual drive.

外部驱动连接器

External Drive Connectors

在外部，单个或大型驱动器组可以连接到单个计算机或工作站。这里最熟悉的可能是通过 USB 连接器连接的单个驱动器（图 18.5）。USB 接口自 1990 年代中期发展以来经历了三种主要的速度配置。第一个标准 USB 1.0 被限制在每秒 12 兆比特左右，这仅对压缩的标准清晰度文件传输有用。更常见的 USB 2.0 能够达到每秒 480 兆比特，并且在今天仍然适用于媒体应用程序。最近的实施，USB 3.0，具有非常可观的每秒 4 吉比特的数据速率，接近内部硬盘驱动器的速度。

Externally, individual or large groups of drives may be connected to a single computer or workstation. The most familiar here may be single drives connected via a USB connector (Figure 18.5). The USB interface has seen three major speed configurations since its development in the mid 1990’s. The first standard USB 1.0 was limited to about 12 megabits per second, which was only useful for compressed standard definition file transfer. The more common USB 2.0 was capable of 480 megabits per second and is still useful today for media applications. The most recent implementation, USB 3.0, has a very respectable data rate of 4 gigabits per second, approaching the speed of internal hard drives.

图 18.5 USB 数据线和通用 USB 标志

Figure 18.5 USB Cable and Universal USB Logo

连接外部驱动器的第二种常见方法是 eSATA。这与用于内部驱动器的电气连接相同，唯一的区别是连接器的形状。这使外部驱动器和驱动器阵列能够像在主机内部一样传输数据。

A second common method for attaching external drives is eSATA. This is the same electrical connection used for internal drives, the only difference being the shape of the connector. This gives external drives and drive arrays the ability to transfer data as if they were inside the host computer.

您可能熟悉的其他连接方法是 FireWire 和 Thunderbolt。FireWire 是一种较旧的连接方法，其速度可与 USB 2.0 相媲美。这种格式由 Apple 开发，在较新的计算机上已被 Thunderbolt 取代（图 18.6）。Thunderbolt 连接速度非常快——高达每秒 20 Gb。

Other connection methods you may be familiar with are FireWire and Thunderbolt. FireWire is an older connection method whose speed is comparable to USB 2.0. This format was developed by Apple, and has been replaced on newer computers by Thunderbolt (Figure 18.6). A Thunderbolt connection is very fast—up to 20 gigabits per second.

存储区域网络

Storage Area Networks

图 18.6 FireWire 800 电缆和 Thunderbolt 电缆

Figure 18.6 FireWire 800 Cable and Thunderbolt Cable

基于文件的工作流的主要先决条件之一是文件需要由多个用户共享。虽然可以从直接连接的系统共享文件，但效率更高 共享是通过为此目的而构建的技术完成的。执行此操作的一种方法是通过 SAN 或存储区域网络。

One of the principal prerequisites for file-based workflows is that files need to be shared by multiple users. While it is possible to share files from direct attached systems, it is more efficient when the sharing is done by technologies built for that purpose. One method of doing this is via a SAN, or Storage Area Network.

SAN 的主要原则之一是它是一个围绕文件存储设计的独立网络。与也连接到大多数系统的普通以太网网络不同，SAN 只有一项工作——处理存储访问。除了硬件之外，在单独的计算机或其中一台客户端计算机上运行的管理程序也可以管理文件。

One of the chief principles of a SAN is that it is a separate network designed around file storage. Unlike the common Ethernet network that is also attached to most systems, the SAN has only one job—to deal with storage access. In addition to the hardware, a management program run on a separate computer or one of the client computers manages the files.

当多个用户访问文件时，共享存储系统会面临一个问题。虽然每个人都可以毫无问题地读取文件，但如果多台计算机同时尝试写入文件，则该文件将会损坏。SAN 管理器软件的工作是仲裁谁有权写入文件。此功能称为锁定，可以通过几种不同的方式发生。第一个，卷锁定，表示第一个连接到驱动器卷的人可以读取和写入它包含的文件。所有其他用户只能读取这些文件。

Shared storage systems face a problem when multiple users are accessing files. While everyone can read a file without issue, if more than one computer tries to write to a file at the same time, that file will be corrupted. It is the job of the SAN manager software to arbitrate who has permission to write to the file. This function, known as locking, can happen in a few different ways. The first, volume locking, says that the first person to connect to a drive volume can both read and write the files it contains. All other users may only read the files.

向下移动到较低级别，SAN 系统可以使用文件夹锁定，这样只有给定文件夹中的第一个用户具有写入权限，但该卷上的其他文件夹可供其他用户写入。

Moving down to a lower level, SAN systems may use folder locking, such that only the first user in a given folder has write permission, but other folders on that volume are available to be written by other users.

最后，每个文件都可以单独锁定，这样只有一个用户可以写入它们。随着要保护的事物（例如卷、文件夹或文件）数量的增加，进入层次结构的每一步都需要更多的计算。

Finally, each file may be individually locked so that only one user may write to them. Each step into the hierarchy is more computationally intense as the number of things to be protected, such as volumes, folders or files, increases.

虽然 SAN 非常高效，但它们要求每台客户端计算机都有一个专门的接口来连接到 SAN。每个客户端还必须运行一个软件以允许访问 SAN，并且必须安装从 SAN 到每台计算机的特殊电缆。这使得 SAN 变得有些昂贵并且难以安装和维护，通常将它们的使用限制在大型组织中。

While SANs are very efficient, they require that each client computer has a specialized interface for the connection to the SAN. Each client must also run a piece of software to allow access to the SAN, and special cabling to each computer from the SAN must be installed. This makes SANs somewhat expensive and difficult to install and maintain, typically limiting their use to large organizations.

网络附加存储

Network Attached Storage

网络附加存储设备通常是将一个或多个硬盘驱动器与一台小型服务器计算机组合在一个盒子中的小型设备。一旦插入计算机网络，它们就提供该网络成员可以访问的外部存储。虽然这些设备是共享文件的便捷方式，但它们通常不够稳健，无法提供实时播放和记录高数据率媒体所需的访问速度。

Network attached storage devices are typically small appliances that combine one or more hard drives with a small server computer in a single box. Once plugged into a computer network, they provide external storage that is accessible to members of that network. While these appliances are a convenient way to share files, they typically are not robust enough to provide the access speeds needed for real-time playback and recording of high data rate media.

服务器

Servers

集中式硬盘驱动器组或存储系统可用于同时为各种用户提供数据。这些存储系统称为服务器。服务器有多种形式，从简单的双硬盘单元到包含数百个磁盘的复杂组，它们有多种用途。例如，一旦新闻镜头被加载到服务器上，全世界的记者和编辑就可以在它被记录在服务器磁盘上的那一刻访问该镜头。数据可以被复制、更改和由多个用户单独存储而不影响原始数据，从而为用户提供速度和灵活性。服务器通过标准以太网连接到客户端计算机或用户。

Centralized groups of hard drives, or storage systems, can be used to provide data for a variety of users simultaneously. These storage systems are called servers. Servers come in many forms, from simple twin hard drive units to complex groups containing hundreds of disks, and they have a variety of uses. For example, once news footage is loaded onto a server, access to that footage would be available to reporters and editors worldwide the instant it was recorded on the servers’ disks. The data can be copied, changed, and stored separately by multiple users without affecting the original data, thereby providing speed and flexibility to the users. Servers are connected to client computers, or users, by standard Ethernet networks.

网络文件服务器

Network File Servers

规模更大的是提供全球数据通信基础设施的文件服务器和数据存储系统。使用 YouTube 和 Netflix 等服务通过 Internet 移动和共享媒体内容是很有可能的。虽然这个公共网络非常适合最终交付给观众，但对于媒体制作和管理来说，它通常不够强大。（有关流媒体的更多信息，请参阅第 21 章。）

On a much larger scale are the file servers and data storage systems that provide the infrastructure of global data communications. It is quite possible to move and share media content over the Internet with services such as YouTube and Netflix. While this public network is fantastic for final delivery to the viewer, it is generally not robust enough for media production and management. (For more information on streaming media, see Chapter 21.)

企业级媒体组织，如电视网络或有线电视公司，通常会通过租用地点之间的连接并在其设施中进行仔细的内部设计来构建自己的数据网络（图 18.7 ）。这些网络与公共 Internet 分开，并且仅用于其所有者的数据流量。如果实施得当，这些网络可以为除要求最苛刻的媒体应用之外的所有媒体应用提供必要的存储和带宽。

Enterprise-scale media organizations, such as TV networks or cable companies, will often build their own data networks with leased connectivity between locations and careful internal design at their facilities (Figure 18.7). These networks are separate from the public Internet and devoted to data traffic only from their owners. When properly implemented, these networks can provide the necessary storage and bandwidth for all but the most demanding of media applications.

云端

The Cloud

作家亚瑟·C·克拉克说：“任何足够先进的技术都与魔法无异。” 云似乎就是这样。借助 Google Drive、Dropbox 和许多其他服务，文件可以在不知道文件存储位置或存储方式的用户之间共享。当然，它们驻留在数据中心的磁盘集群上，靠近便宜的电力和充足的带宽（图 18.8）。虽然公共网络尚未提供数据速度

The author Arthur C. Clark said, “Any sufficiently advanced technology is indistinguishable from magic.” The cloud seems to be just that. With services like Google Drive, Dropbox and many others, files may be shared among users who will have no idea where or how they are stored. Of course they reside on disk clusters in data centers somewhere near cheap power and plentiful bandwidth (Figure 18.8). While public networks do not yet provide the data speeds

图 18.7 网络服务器机房

Figure 18.7 Network Server Room

图 18.8 云网络

Figure 18.8 Cloud Network

为了使这些对更高质量的实时媒体操作有用，那一天可能很快就会到来。也许从本书编写到您拿起这本书时，它就已经发生了。

to make these useful for real time media operations at higher qualities, that day may come soon. Perhaps it happened from the time this book was written until you picked it up.

在云中存储内容有一些吸引力和一些缺点。内容所有者可能永远不必考虑对基于云的资产进行维护、升级或备份。所有这些都是您租用空间的租赁费用的一部分。

Storing content in the cloud has some appeals and some drawbacks. The content owner may never have to consider maintenance, upgrades or backups of cloud-based assets. All that is part of the lease costs for the space that you rent.

另一方面，资产在公网上，数据安全更难保障。对于许多拥有基于向观众收取内容费用的商业模式的大型组织而言，这是一个主要的绊脚石。云服务，因为它们通常在地理上远离用户，如果它们必须提供实时媒体访问，也需要昂贵的高带宽连接。

On the other hand, data security is harder to guarantee as the assets are on the public network. And for many large organizations, those who have business models based on charging viewers for content, this is a major stumbling block. Cloud services, because they are normally geographically distant from the user, also require expensive high bandwidth connections if they must provide real time media access.

概括

Summary

自世纪之交以来，音频和视频的工作流程发生了巨大的变化。基于文件的存储和管理已经取代了主导该行业半个多世纪的基于录像带的工作流程。以文件形式提供的内容一直受到分发渠道增长的推动和促进。电视最初只能作为在客厅观看的广播，现在可以在各种不同的物体上使用，从手机到平板电脑，再到环绕在建筑物外部的屏幕。

The workflow of audio and video has undergone a huge change since the turn of the century. File-based storage and management has replaced the videotape-based workflows that dominated the industry for more than half a century. Having content available as files has been driven by, and facilitated, the growth of distribution channels. Initially only available as a broadcast to be viewed in a living room, TV can now be consumed on a variety of different objects from phones, to tablets, to screens that are wrapped around the outside of buildings.

文件容器

File Containers

媒体文件结合了音频、视频和元数据。正如您需要一个信封才能使用美国邮政服务一样，媒体文件也需要一个容器或包装器来封装数据，以便在计算机系统中存储和移动它。正如物理信封有不同的形状、大小和材料以适应不同的任务一样，有许多媒体容器可以存储和移动媒体数据（图 19.1）。

Media files combine audio, video and metadata. Just as you need an envelope to use the U.S. Postal Service, media files need a container or wrapper to encapsulate data to store and move it within computer systems. And just as physical envelopes come in different shapes, sizes and material suited to various tasks, there are a number of media containers that store and move media data (Figure 19.1).

图 19.1 封装过程

Figure 19.1 Encapsulation Process

媒体容器所做的最重要的事情之一是排列和交错数据，以便音频和视频同步播放。如果所有视频数据都在文件的开头，则 最后的音频，整个文件需要加载到计算机内存中才能播放。大多数电脑没有足够的内存来做这件事，观众也没有耐心等待这一切发生。让我们来看看不同的文件容器。

One of the most important things a media container does is arrange and interleave the data so that the audio and video play out synchronically. If all the video data were at the start of the file, with the audio at the end, the entire file would need to be loaded into the computer memory before it could be played. Most computers don’t have enough memory for this, nor does the audience have the patience to wait for this to happen. Let’s take a look at different file containers.

WebM

WebM

此容器是与 HTML 5 计划相关的 Web 文件分发的最新开发。虽然它支持有限的编解码器，但它在某些领域取得了进展，例如 YouTube 等大型服务以这种格式提供其内容（图 19.2）。（本章稍后将更详细地讨论 WebM。）

This container is a more recent development for distribution of web files in association with HTML 5 initiatives. While this supports limited codecs, it is making headway in some areas with large services like YouTube making their content available in this format (Figure 19.2). (WebM is discussed in more detail later in this chapter.)

图 19.2 文件容器格式

Figure 19.2 File Container Formats

其他容器

Other Containers

除了所讨论的容器之外，还有许多其他容器。有些是正在逐渐停止使用的旧版格式。其他的是全新的，尚未建立庞大的用户群。有些是特殊用途，仅限于设备和工作流程。

There are many other containers beyond those discussed. Some are legacy formats that are fading from use. Others are brand new and have yet to build a large user base. Some are special purpose and limited to equipment and workflows.

切换容器

Switching Containers

在容器之间移动媒体的过程称为重新包装。音频和视频保持不变，仍然是原始编解码器。材料只是在更适合目标设备的不同容器中重新组织。例如，当文件从相机移动到编辑系统时，这个过程经常发生。

The process of moving media between containers is referred to as re-wrapping. The audio and video stay the same, still in the original codecs. The material is just reorganized in a different container better suited to the target device. For example, this process frequently happens when files are moved from the camera to an editing system.

编解码器

Codecs

正如您在第 14 章中了解到的，数据通常被压缩以减少我们的计算机必须处理的信息量。有许多不同的算法或编解码器可用于这项工作。有些最适合在捕获图像时使用，而另一些则用于编辑。有些适用于分发，具有承载它们的媒体类型的变体。为一种目的开发的编解码器通常也用于其他领域。

As you learned in Chapter 14, data is normally compressed to reduce the amount of information with which our computers have to cope. There are many different algorithms, or codecs, that can be used for this job. Some are best suited for use when capturing images, while others are meant for editing. Some work well for distribution, with variants for the kind of medium that will carry them. Often codecs developed for one purpose are also used in others areas.

已经创建了数百种编解码器，更新更高效的编解码器取代了前几代。让我们看一下在制作和后期制作过程，以及用于流媒体的过程。

There are hundreds of codecs that have been created, with newer more efficient ones replacing previous generations. Let’s take a look at some of the more common codecs that are used in the production and post production process, as well as those used to stream media.

采集编解码器

Acquisition Codecs

从照相手机到专为数字电影质量设计的相机，Image Capture 有多种形式。低端相机寻找允许将长时间捕获存储在小空间中的编解码器。高端的目标是捕捉尽可能多的细节，以便在后期制作图像处理中实现最大的灵活性。

Image Capture comes in many forms from the camera phone through cameras designed for digital cinema quality. Low-end cameras look for codecs that allow long captures to be stored in a small space. The goal at the high end is to capture as much detail as possible to allow the greatest flexibility in post production image processing.

高端是 ArriRaw 和 Redcode 等编解码器。他们生产的相机的 Arri 格式根本没有压缩，顾名思义，它是来自图像传感器的原始数据。来自 Red Camera 系列制造商的 Red-code 在使用 JPEG 2000 小波压缩的编解码器中被非常温和地压缩。Sony 还提供一种采用 SR 格式的轻度压缩采集编解码器。虽然这些编解码器生成的文件很大，但它们包含传感器捕获的所有数据。对于合成和颜色分级等后期制作操作，所有可用的细节都提供了更大范围的创意选择。

At the high end are codecs such as ArriRaw and Redcode. The Arri format for the cameras they produce is not compressed at all and is, as the name implies, the raw data from the image sensor. Red-code, from the makers of the Red Camera series, is compressed, very gently, in a codec that uses JPEG 2000 wavelet compression. Sony also offers a gently compressed acquisition codec in their SR format. While the files these codecs produce are huge, they contain all the data captured by the sensor. For later post production manipulations like compositing and color grading, all the available detail gives a greater range of creative options.

Adobe 创建了 CinemaDNG 格式作为用于图像捕获的开放非专有格式。这是他们的数字负片格式（或 DNG）的移动图像版本，支持温和的无损压缩。一些相机制造商支持这种格式，包括 Black Magic。

Adobe created CinemaDNG format as an open non-proprietary format for image capture. This is a moving image version of their Digital Negative Format (or DNG), which supports gentle lossless compression. Several camera makers support this format including Black Magic.

使用最初设计用于编辑的编解码器可以捕获压缩程度更高的图像。Avid DNxHD 和 Apple ProRes 就是两个例子。这两种格式都允许通过选择不同的数据速率进行各种质量的捕获。这些编解码器最初是为编辑而创建的，将每个帧捕获为一个单独的元素。两者都具有大约 200–250 兆位每秒 (Mbps) 的最高数据速率，或大约 7:1 的压缩比。除了机内录制，这些也是录制演播室电视节目的视频服务器的流行选择，通常数据速率低至每秒 100 兆比特。使用这些格式的另一个动机是捕获的材料可以编辑。无需额外处理即可为编辑室做准备。剪辑文件可以简单地快速复制到编辑系统。明显地，

A somewhat more compressed image can be captured using codecs that were originally designed for editing. Avid DNxHD and Apple ProRes are two examples. Both of these formats allow for various quality captures by choosing different data rates. Originally created for editing, these codecs capture each frame as a separate element. Both have top data rates of about 200–250 Megabits per second (Mbps), or about 7:1 compression ratio. In addition to on-camera recording, these are popular choices for video servers recording studio television shows, often with data rates as low as 100 Megabits per second. An additional motivation to use these formats is that the captured material is edit-ready. No additional processing is necessary to prepare for the edit room. The clip files may simply be quickly copied to the edit system. Obviously, this is tremendously helpful for workflows that have short deadlines.

质量阶梯的下一步是采用压缩率更高的格式录制的摄像机，例如 Sony XDCam 和 Panasonic AVCHD。这些格式的数据速率在每秒 30 到 50 兆位之间。这两种压缩类型都是 MPEG 4 Part 10 或 H.264 格式的变体。此类相机通常用于新闻采访和其他不需要大量图像合成或颜色分级的项目。由于这些图像中的大部分细节都被压缩了，因此它们不适合进行繁重的后期制作操作。

The next step down the quality ladder is to cameras that record in more heavily compressed formats such as Sony XDCam and Panasonic AVCHD. The data rate for these formats is in the 30 to 50 Megabits per second range. Both compression types are variations of the MPEG 4 Part 10, or H.264 format. Cameras in this class are often used in newsgathering and other projects that do not require heavy image compositing or color grading. Since much of the detail is compressed out of these images, they are not suited to heavy post production manipulation.

最后，在图像捕捉范围的低端是使用非常长的 GOP 版本的编解码器（如 H.264）进行录制的摄像机。这些图像的压缩非常有损，数据速率通常低于 1 Mbps。虽然这些可以生成可接受的图像，但在后期制作中很难使用它们，而且通常必须转码为不同的格式才能进行编辑。作为消费设备销售的照相电话和廉价数码摄像机属于此类设备。

Finally at the lower end of the image capture spectrum are cameras that record in very long GOP versions of codecs like H.264. Compression for these images is very lossy, with data rates often less than 1 Mbps. While these can produce acceptable images, they are very difficult to work with in post production and often must be transcoded to a different format for editing. Camera phones and inexpensive digital video cameras sold as consumer devices fall into this group of equipment.

后期制作中使用的编解码器

Codecs Used in Post Production

如前所述，有些编解码器是专门为满足编辑的独特要求而设计的。例如，Avid 创建了一组称为 DNxHD 的编解码器，而 Apple 的工程师已经制作了几个版本的 ProRes 编解码器（图 19.3）。这两种都是基于帧内的编解码器，这意味着它们不需要来自相邻帧的信息来生成图像。

As mentioned earlier, there are codecs that were designed specifically for the unique requirements of editing. As examples, Avid created a group of codecs called DNxHD, while the engineers at Apple have produced several versions of their ProRes codecs (Figure 19.3). Both of these are Intraframe-based codecs, meaning they do not require information from adjacent frames to produce images.

许多编解码器通过利用相邻帧中的冗余信息来实现高压缩比。这确实使编辑成为一项挑战。为了在特定帧处进行剪切，计算机必须通过从相邻帧解码图片来创建该帧以及随后的新帧。虽然这是可能的，但它会给系统带来一定的负担，并且会给进行编辑的人带来不尽如人意的体验。

Many codecs achieve high compression ratios by taking advantage of redundant information in adjacent frames. This does make editing a challenge. In order to make a cut at a specific frame, the computer must create that frame, along with the new one that follows, by decoding the picture from neighboring frames. While this is possible, it is somewhat taxing on the system and can produce a less than satisfactory experience for the person making the edits.

图 19.3 使用 .MOV 文件容器格式的各种编解码器

Figure 19.3 Various Codecs Using .MOV File Container Format

虽然有专为编辑而设计的编解码器，但大多数编辑程序也可以与许多其他编解码器一起使用。为了工作流程的速度和简单性，剪辑师通常会选择在其素材采集时使用的编解码器中工作。例如，一些较大的网络和节目制作人已将每秒 50 兆比特的 XDCam 作为他们的通用格式。这在质量、速度和可操作性之间提供了可接受的折衷。

While there are codecs designed just for editing, most edit programs will work with many other codecs as well. Often editors will choose to work in the codec that their material was acquired in for speed and simplicity in workflow. For example, some larger networks and program producers have settled on XDCam at 50 Megabits per second as their common format. This offers an acceptable compromise between quality, speed and operability.

贡献和夹层编解码器

Contribution and Mezzanine Codecs

通常需要一种介于未压缩素材和分发编解码器之间的压缩。例如，假设体育赛事中的摄像机正在捕捉 RAW 或未压缩的素材。当需要上传该素材或通过光纤线路将其发送回网络时，必须压缩信号以减小其文件大小。执行此操作的编码器设置为通道可以处理的最大压缩比。该压缩级别称为贡献质量. 当然，当镜头到达网络时，它可能会进一步压缩以记录在服务器上，或者它可能会被解压缩以与其他素材切换为实时信号。贡献质量压缩的其他用途包括存储和播放节目内容和商业广告，以及存档完成的作品。

Frequently there is a need for compression that is an intermediate between uncompressed footage and distribution codecs. For example, let’s say the cameras at a sports event are capturing the footage RAW or uncompressed. When it’s time to uplink that footage or send it over a fiber optic line back to the network, the signal has to be compressed to reduce its file size. The encoder that does that is set to the largest compression ratio the channel can handle. That level of compression is referred to as contribution quality. Of course, when the footage gets to the network, it might be further compressed to be recorded on a server, or it might be uncompressed to be switched with other material as a live feed. Other uses of contribution quality compression include storing and playing out program content and commercials, and archiving finished work.

用于此类压缩的另一个名称是夹层。就像夹层位于建筑物楼层之间的中间位置一样，您可以将夹层压缩视为中间层压缩。此类压缩的一种常见用途是为 YouTube 等分发渠道准备文件。在编辑编解码器中为一个小时的节目完成的编辑可以运行到许多千兆字节，太大而无法轻松发送到网络主机。进行压缩是为了将数据量减少到更容易上传的程度。Web 托管站点然后将该文件处理成不同比特率的几个变体，以使其公开可用。该网站将为每个用户的连接提供自动或手动选择最佳比特率。因此，您发送要重新编码的是中间格式或夹层格式。

Another name used for this type of compression is mezzanine. Much like the mezzanine is half way between floors in a building, you can think of mezzanine compression as a middle level of compression. One common use of this type of compression is when preparing files for distribution channels such as YouTube. The finished edit in the edit codec for an hour-long show can run to many Gigabytes, far too large to easily send to the web host. A compression is made to reduce the amount of data to something easier to upload. The web host site then processes that file into several variations at different bit rates to make it publically available. The web site will offer either automatic or manual selection of the best bit rate for each user’s connection. Thus, what you have sent to be re-encoded is a middle or mezzanine format.

数字分发编解码器

Digital Distribution Codecs

对于第 21 章中更详细讨论的互联网流媒体等数字分发，某些格式比其他格式更有效。特别是一种编解码器，MPEG-4，是专门为计算机上的流媒体开发的，其信号吞吐量或带宽比数字电视或 DVD 低得多。它对三个特定领域产生了重大影响，即交互式多媒体（通过磁盘和网络分发的产品）、交互式图形应用程序（例如，移动应用程序“愤怒的小鸟”）和数字电视 (DTV)。

For digital distribution such as Internet streaming, which is discussed in more detail in Chapter 21, there are certain formats that are more effective than others. One codec in particular, MPEG-4, was developed especially for streaming media on computers that have a much lower signal throughput or bandwidth than digital television or DVDs. It has heavily influenced three specific areas, which are interactive multimedia (products distributed on disks and via the web), interactive graphic applications (for example, the mobile app “Angry Birds”) and digital television (DTV).

MPEG-4 编解码器

MPEG-4 Codecs

MPEG-4 是最常见的数字多媒体格式，用于以比以前的 MPEG-1 或 MPEG-2 方案低得多的数据速率和更小的文件大小流式传输视频和音频。它可以流式传输以前 MPEG 方案中包含的所有内容，但它得到了极大的扩展，以支持视频和音频对象、3D 内容、​​字幕和静止图像以及其他媒体类型——所有这些都采用低比特率编码方案。它支持很多从手机到卫星电视分配器（例如 DISHTV 和 DIRECTV）的设备，再到广播数字电视。MPEG-4 有许多细分，称为配置文件，适用于从具有低图像质量和低分辨率的监控摄像机到更复杂的 HDTV 广播和具有更高质量图像和更高分辨率的蓝光 DVD 的应用。让我们仔细看看一些 MPEG-4 配置文件。

MPEG-4 is the most common digital multimedia format used to stream video and audio at much lower data rates and smaller file sizes than the previous MPEG-1 or MPEG-2 schemes. It can stream everything included in the previous MPEG schemes, but it was expanded greatly to support both video and audio objects, 3D content, subtitles and still images as well as other media types—all with a low bitrate encoding scheme. It supports a great many devices from cell phones to satellite television distributors, such as DISHTV and DIRECTV, to broadcast digital television. MPEG-4 has many subdivisions, called profiles, that address applications ranging from surveillance cameras with low-image quality and low-resolution to more sophisticated HDTV broadcasting and Bluray DVDs that have a much higher quality image and greater resolution. Let’s take a closer look at some MPEG-4 profiles.

H.264/AVC（高级视频编码）是主要 MPEG-4 配置文件的一部分。它是该配置文件中最流行的视频编解码器或视频压缩格式之一，用于从 Internet 流媒体应用程序到 HDTV 广播、蓝光 DVD 甚至数字电影的所有内容。它几乎是无损的，节省了 50% 的比特率，同时仍保持出色的视频质量。2008 年，H.264 在美国获准用于广播电视。这对受带宽问题限制的数字卫星电视特别有帮助。H.264 的比特率不到其前身 MPEG-2 的一半。

H.264/AVC (Advanced Video Coding) is part of the main MPEG-4 profile. It is one of the most prevalent video codecs or video compression formats in that profile and is used for everything from Internet streaming applications to HDTV broadcast, Blu-ray DVDs and even Digital Cinema. It is nearly lossless with a 50% bit rate savings while still maintaining excellent video quality. In 2008, H.264 was approved for use in broadcast television in the United States. This was especially helpful to Digital Satellite TV, which is constrained by bandwidth issues. H.264 is less than half of the bitrate of its MPEG-2 predecessor.

高效视频编码，也称为 HEVC/H.265，是 H.264/AVC 的继承者。与 H.264 相比，这种新的视频压缩编解码器将数据压缩率提高了一倍，在保持相同水平的视频质量的同时又节省了 50% 的比特率。或者，它可以用于以与 H.264 相同的比特率提供大大改进的视频质量。

High Efficiency Video Coding, also known as HEVC/H.265, is the successor to H.264/AVC. Compared to H.264, this new video compression codec doubles the data compression ratio squeezing out another 50% bitrate savings while still maintaining the same level of video quality. Alternatively, it can be used to provide vastly improved video quality at the same bit rate as H.264.

与 Apple 的 QuickTime 不同，H.265 使用的包装器或交付容器称为 DivX。这是最新的视频压缩标准，于 2013 年完成并发布。它还可以支持 8K UHD（超高清）电视和高达 8192 × 4230 的分辨率。在撰写本书时仍处于早期阶段，H .265 承诺提供对增强视频格式、可缩放编码和 3D 视频扩展的支持。

Unlike Apple’s QuickTime, the wrapper or delivery container that H.265 uses is called DivX. This is the newest video compression standard, which was completed and published in 2013. It can also support 8K UHD (Ultra High Definition) televisions and resolutions up to 8192 × 4230. Still in its early stages as of the writing of this book, H.265 promises to deliver support for enhanced video formats, scalable coding and 3D video extensions.

谷歌的 WebM 编解码器

Google’s WebM Codec

Google 的 WebM 则完全不同。与其他专有编解码器不同，Google 的 WebM 是一种音频-视频媒体容器格式，不仅免版税，而且还被认为是用于 HTML5 的开源视频压缩方案。这种格式是通过社区驱动的流程开发的，该流程已完全记录并公开供查看。WebM 不包含专有扩展，所有用户都被授予全球性、非排他性、免费、免版税的专利许可。

Google’s WebM is quite a different story. Unlike other proprietary codecs, Google’s WebM is an audio-video media container format that is not only royalty free, but it is also considered to be an open-source video compression scheme for use with HTML5. This format is being developed through a community driven process that is fully documented and publicly available for viewing. WebM does not contain proprietary extensions and all users are granted a worldwide, non-exclusive, no-charge, royalty-free patent license.

HTML5 视频最重要的方面之一是它包含各种标签，允许浏览器在不需要 Flash 或 Silverlight 等插件的情况下本地播放视频，并且它没有指定要使用的标准编解码器。

One of the most important aspects of HTML5 video is that it includes various tags that allow browsers to natively play video without requiring a plug-in like Flash or Silverlight, and it does not specify a standard codec to be used.

音频编解码器

Audio Codecs

正如有多种视频编解码器一样，也有许多针对不同目的而创建的音频编解码器。

Just as there is a variety of video codecs, there are numerous audio codecs that have been created for different purposes.

MP3是一种用于编码数字音频的有损数据压缩方案。MP3 是事实上的数字音频压缩方案，用于在大多数数字音频播放器（如 iPod）上传输和播放音乐。它是一种由运动图像专家组 (MPEG) 设计的特定音频格式，可大大减少忠实再现人耳所感知的录音所需的数据量。用于产生这些结果的方法称为感知编码。

MP3 is a lossy data compression scheme for encoding digital audio. MP3 was the de facto digital audio compression scheme used to transfer and playback music on most digital audio players such as iPods. It is an audio-specific format designed by the Moving Picture Experts Group (MPEG) to greatly reduce the amount of data required to faithfully reproduce an audio recording as perceived by the human ear. The method used to produce these results is called perceptual encoding.

在感知编码中，压缩算法用于通过丢弃人耳无法感知的音频数据来降低音频数据流的带宽。例如，一个响亮声音之后的柔和声音将从音频信号节省带宽中删除。

In perceptual encoding, compression algorithms are used to reduce the bandwidth of the audio data stream by dropping out the audio data that cannot be perceived by the human ear. For example, a soft sound immediately following a loud sound would be dropped out of the audio signal saving bandwidth.

AAC（高级音频编码）是一种用于数字音频的有损压缩和编码方案，正在取代 MP3。AAC 音频使用比 MP3 更复杂的压缩算法，在与 MP3 相似的比特率下具有更好的音频质量。

AAC (Advanced Audio Coding) is a lossy compression and encoding scheme for digital audio, which is replacing MP3. Using a more sophisticated compression algorithm than MP3, AAC audio has a vastly better audio quality at similar bit rates as MP3.

作为普遍使用的 MPEG-2 和 MPEG-4 系列标准的一部分，AAC 已成为 iPhone、iPod、iTunes、YouTube、任天堂 3D 和 DSi、Wii、PlayStation 3 和DivX Plus 网络播放器（图 19.3）。能够接收 Sirius XM 的车载音响系统制造商也正在放弃 MP3，转而采用 AAC 音频。

As part of the pervasive MPEG-2 and MPEG-4 family of standards, AAC has become the standard audio format for devices and delivery systems such as iPhone, iPod, iTunes, YouTube, Nintendo 3Ds and DSi, Wii, the PlayStation 3 and the DivX Plus Web Player (Figure 19.3). The manufacturers of in-dash car audio systems, capable of receiving Sirius XM, are also moving away from MP3 and are embracing AAC audio.

Windows Media Audio (WMA) 是 Microsoft 开发的专有有损音频编解码器，用于与 MP3 和 RealAudio 编解码器竞争。它由 Windows Media Player 使用。它的变体与其他几个 Windows 或 Linux 播放器兼容。这种音频格式和编解码器可以使用 Quick-Time 框架在 Mac 上播放，但它需要一个名为 Flip4Mac WMA 的第三方 QuickTime 组件才能播放。

Windows Media Audio (WMA) is a proprietary lossy audio codec developed by Microsoft to compete with MP3 and the RealAudio codecs. It is used by the Windows Media Player. Variations of it are compatible with several other Windows or Linux players. This audio format and codec can be played on a Mac using the Quick-Time framework but it requires a third-party QuickTime component called Flip4Mac WMA in order to play.

分发编解码器

Distribution Codecs

分发编解码器是为向观众提供内容而调整的编解码器。它们通常是压缩程度更高的编解码器版本，例如 MPEG-2、H.264 和 HEVC。这里的选择基于尽可能减少带宽，同时为不太完美的信号路径提供强大的错误恢复。选择的编解码器是传送通道类型的函数。

Distribution codecs are the ones that are tuned for delivering the content to the audience. Often they are more heavily compressed versions of codecs such as MPEG-2, H.264 and HEVC. Here the selection is based on reducing bandwidth as much as possible while providing robust error recovery for less than perfect signal paths. The codec that is selected is a function of the type of delivery channel.

对于无线 (OTA) 电视，ATSC 选择了每秒 19 兆比特以上的 MPEG-2。2009 年修订的 ATSC 标准也允许使用更高效的 H.264 编解码器。在撰写本书时，ATSC 正在努力标准化下一个广播格式，以包括 UHD 或 4K 视频。正在考虑的编解码器是 HEVC 或 H.265，即所谓的 ATSC 3。

For Over the Air (OTA) television, MPEG-2 at just over 19 Megabits per second was chosen by the ATSC. A 2009 revision of the ATSC standard also allowed the more efficient H.264 codec to be used as well. As this book was being written, the ATSC was working to standardize the next broadcast format to include UHD, or 4K video. The codec being considered is HEVC or H.265 for what will be known as ATSC 3.

当通过电缆和卫星传送到家庭时，视频会使用 MPEG 编解码器进行压缩。然而，与 OTA 相比，有线和卫星公司通常会提供压缩率更高的内容，以便为订户提供更多频道。

When delivered over cable and satellite to the home, the video is compressed using MPEG codecs. However when compared to OTA, cable and satellite companies often provide more highly compressed content in an effort to deliver more channels to subscribers.

光盘使用 MPEG-2 或 H.264。MPEG-2 通常出现在 DVD 上，它们始终是标准清晰度。蓝光光盘可以使用多种编解码器——MPEG-2、H.264 或 Windows Media (VC-1)。

Optical disks use either MPEG-2 or H.264. MPEG-2 is normally seen on DVDs, which are always standard definition. Blu-Ray disks can use several codecs—MPEG-2, H.264, or Windows Media (VC-1).

YouTube 以 MPEG-4 格式压缩内容。每个提交的视频都以不同的大小制作多个副本，用户可以选择其连接和计算机支持的播放质量。一些在线服务，例如 Netflix，会根据带宽条件在不同的压缩级别之间动态变化。其他在线分发可以使用范围广泛的编解码器，包括 Windows Media、所有 MPEG 变体、H.264、HEVC 等等。

YouTube compresses content in MPEG-4. Several copies of each submitted video are made at different sizes, and the user can select the quality of the playback supported by their connection and computer. Some online services, such as Netflix, dynamically change between different compression levels based on bandwidth conditions. Other online distribution can use a broad range of codecs including Windows Media, all the MPEG variants, H.264, HEVC, and many others.

压缩标准、编解码器和容器的开发是一个持续的过程。正如数学家和工程师所说利用计算机和网络速度的优势，将会开发出新的更好的压缩技术。

The development of compression standards, codecs and containers is an ongoing process. As mathematicians and engineers take advantage of computer and network speed, new and better compression technologies will be developed.

光媒体

Optical Media

虽然模拟视频主要是使用录像机中的录像带以磁性方式记录的，但数字视频信号可以电子、磁性或光学方式存储。光学媒体是数字领域的发展。它不用于模拟记录或存储，仅用于记录或存储数字数据。磁介质和光介质之间的主要区别在于磁介质易失性，这意味着信息可能会因暴露在强磁场中而意外丢失。另一方面，光学介质是非易失性的。数据一经记录，除非用户直接操作，否则无法更改或删除。

While analog video was primarily recorded magnetically using videotape in a videotape machine, the digital video signal can be stored electronically, magnetically or optically. Optical media is a development of the digital domain. It is not used for analog recording or storage, only for recording or storing digital data. The primary difference between magnetic and optical media is that magnetic media are volatile, meaning that the information can be lost accidentally by exposure to a strong magnetic field. Optical media, on the other hand, are non-volatile. The data, once recorded, cannot be changed or erased except through direct action by the user.

光刻录

Optical Recording

所有光学媒体都使用激光技术来记录、存储和再现数字数据。激光系统由三个主要部件组成：激光器、镜头和记录介质。让我们来看看它们是如何协同工作的。

All optical media use laser technology for recording, storing, and reproducing digital data. There are three primary components of a laser system: a laser, a lens, and the recording media. Let’s take a look at how they work together.

图 20.1 相干和非相干光频率

Figure 20.1 Coherent and Incoherent Light Frequencies

普通光，例如灯泡，被称为非相干光。非相干光由向各个方向散射的多个频率组成。激光器是一种以光束形式产生相干光的光学设备（图 20.1）。相干光具有单一的特定频率。当电流用于激发或激发化合物时，会产生激光束。 特定的化学物质会发出特定频率的光。因此，激光束是单一的、特定频率的相干光。

Ordinary light, such as a light bulb, is referred to as incoherent light. Incoherent light is composed of multiple frequencies that are scattered in all directions. A laser is an optical device that generates coherent light in the form of a beam (Figure 20.1). Coherent light has a single, specific frequency. A laser beam is created when electrical current is used to energize or excite a chemical compound. Specific chemicals emit specific frequencies of light. Therefore, a laser beam is a single, specific frequency of coherent light.

然后，该光线通过透镜聚焦，该透镜可以由多种透明材料制成。工业级红宝石通常用作透镜材料，占普通激光器的红色。用于创建图像的光能或用于创建声音的声能被转换为电能，然后用于为激光提供能量。

This light is then focused through a lens, which may be made of a variety of transparent materials. Industrial-grade rubies are often used as the lens material, accounting for the red color of common lasers. Light energy used in the creation of an image or acoustical energy used in the creation of sound is converted to electrical energy, which is then used to energize the laser.

光盘由纯聚碳酸酯塑料制成。读取数据需要一个反射表面，这个表面通常是薄薄的铝背衬，偶尔也有金背衬。该层由透明涂层保护，可以在上面贴上印刷标签（图 20.2）。

Optical discs are made from a pure polycarbonate plastic. A reflective surface is required for the purpose of reading the data and this surface is usually a thin backing of aluminum or occasionally gold. This layer is protected by a transparent coating to which printed labels can be applied (Figure 20.2).

从激光源射向存储介质的强光束改变了塑料，数据作为光学介质物理结构的变化而被存储。当激光器通电时，这种变化会产生一个小点或凹坑。激光关闭的区域留下一个平面，也称为平面（图 20.2）。这些凹坑和平面记录在一个圆形轨道中，从磁盘的内部或中心开始，向外向外朝向边缘（图 20.3）。在数据检索中，凹坑和平地之间的变化记录为 1，没有变化记录为零。

The intense beam of light being directed from the laser source to the storage medium changes the plastic and the data is stored as a change in the physical structure of the optical media. This change creates a small spot, or pit, when the laser is energized. An area where the laser is off leaves a flat, also called a land (Figure 20.2). These pits and flats are recorded in a circular track starting from the inside, or center of the disk, going outward toward the edge (Figure 20.3). On data retrieval, the changes between pits and flats are registered as ones, with no change registering as a zero.

图 20.2 CD 截面

Figure 20.2 CD Cross Section

图 20.3 CD 方向流

Figure 20.3 CD Directional Flow

商业预录光盘是使用一种工艺生产的，即在施加反射层之前将凹坑模制或压印到聚碳酸酯中。凹坑是实际的物理凹痕，当光盘播放器读取时，这些凹痕会改变该添加层的反射率。

Commercially pre-recorded optical discs are produced using a process that molds or stamps the pits into the polycarbonate before the reflective layer is applied. The pits are actual, physical indentations that change the reflectivity of this added layer when read by an optical disc player.

消费者可记录光盘在聚碳酸酯层和反射金属层之间具有有机染料或结晶金属合金数据记录层，该层的成分由光盘的格式决定。这层染料或合金被激光加热并产生模拟凹坑产生的变化的物质反射率的变化。

Consumer recordable discs have an organic dye or crystalline metal alloy data recording layer between the polycarbonate layer and the reflective metal layer, the composition of this layer being determined by the format of the disc. This layer of dye or alloy is heated by the laser and produces changes in reflectivity of the substance that mimic the changes produced by the pits.

光学再现

Optical Reproduction

为了从塑料记录介质上读取凹坑和平面，需要反射表面。如前所述，铝或偶尔使用金通常用作反光背衬塑料。铝背衬还可以保护塑料上的数字数据不被损坏。

In order to read the pits and flats from the plastic recording media, a reflective surface is required. As mentioned earlier, aluminum, or occasionally gold, is generally used as the reflective backing against the plastic. The aluminum backing also protects the digital data on the plastic from being damaged.

再现或播放数据时，激光束始终保持打开状态。照射在磁盘表面的恒定光线被背衬反射。背衬还可以保护数字数据不被损坏。该系统解释了平面反射和凹坑反射之间的时间差异。这种时间差异允许系统将信息读取为零或一。

When reproducing or playing back the data, the laser beam remains on constantly. The constant light shining on the surface of the disk is reflected by the backing. The backing also protects the digital data from being damaged. The system interprets the difference in time between a reflection off a flat surface and a reflection off a pit. This difference in time allows the system to read the information as zeros or ones.

光学格式

Optical Formats

光学格式之间的主要区别在于一张光盘上可以存储多少数据。虽然数字数据流以位为单位，但所有数字内存均以字节为单位。高速 Internet 连接以每秒比特数 (bps)来衡量，而 CD 等单面设备可以容纳 650 到 800 MB 或兆字节的数据。

The principal difference among optical formats is how much data can be stored on a single disc. While the flow of digital data is measured in bits, all digital memory is measured in bytes. A high-speed Internet connection is measured as so many bits per second (bps), whereas a single-sided device such as a CD can hold between 650 and 800 MB, or megabytes, of data.

光学介质的类型

Types of Optical Media

CD（光盘）和 DVD（数字多功能光盘或数字视频光盘）是同一类型的光学媒体。格式之间的直接区别之一是存储容量。光学介质上的存储容量是可以存储或写入介质表面的轨道数量的函数。使磁盘上的磁道更窄并使它们靠得更近，就像在 DVD 中一样，可以产生更大的存储容量。在物理上，CD 和 DVD 具有相同的尺寸，通常直径为 120 毫米，但也有直径为 80 毫米的迷你光盘格式。

CDs (compact discs) and DVDs (digital versatile discs or digital video discs) are the same type of optical media. The immediate difference between the formats is one of storage capacity. Storage capacity on optical media is a function of the number of tracks that can be stored or written on the surface of the media. Making the tracks on the disks narrower and placing them closer together, as in DVDs, yields a greater storage capacity. Physically, CDs and DVDs have the same dimensions, usually 120mm in diameter, although there can be minidisc formats with an 80mm diameter.

CD 类型

Types of CDs

CD：CD 主要用于录音、软件和游戏分发、静止图像，以及在一定程度上用于视频。仅由于磁盘的存储容量，在 CD 上记录运动图像是有限的。CD 是单面的，存储容量在 650 到 800 MB 之间。

CD: Primarily, CDs are used for audio recording, software and game distribution, still images, and, to a limited degree, video. Recording of images in motion is limited on CDs only because of the storage capacity of the disk. CDs are single sided and have a storage capacity of between 650 to 800 MBs.

CD-ROM（CD-只读存储器）：CD-ROM 光盘在外观上与其他 CD 光盘相同。CD-ROM 用于音频 CD、计算机游戏和其他软件的商业发行。CD-ROM 是使用玻璃母盘模压和冲压工艺大量生产的。CD-ROM 的存储容量在 650 到 800 MB 之间。

CD-ROM (CD–Read-Only Memory): CD-ROM discs are identical in appearance to other CD discs. CD-ROMs are used for the commercial distribution of audio CDs, computer games and other software. CD-ROMs are mass produced using a process of molding and stamping with a glass master disc. CD-ROMs have a storage capacity of between 650 to 800 MBs.

CD-R（可记录 CD）：这些光盘最初被称为 CD 一次写入 (CD-WO)。采用有机染料层来记录数据。激光有效地燃烧染料，使其变得不透明并反射更少的光。记录层被激光永久改变。CD-R 光盘可以写入一次，但可以多次读取。

CD-R (CD–Recordable): These discs were originally known as CD Write-Once (CD-WO). An organic dye layer is employed to record the data. The laser effectively burns the dye which causes it to become opaque and reflect less light. The recording layer is changed permanently by the laser. CD-R discs can be written to once, but read many times.

CD-RW（CD-可重写）：这些光盘在记录层中使用结晶金属合金。激光将其加热并熔化，形成预录 CD 的凹坑和凸台。CD-RW 光盘最多可以重新录制 1,000 次，但必须在两次录制之间进行空白处理。它们可以被多次阅读。由于用于重写光盘的文件系统，存储容量通常小于 640 MB。

CD-RW (CD–Rewritable): These discs use a crystalline metal alloy in the recording layer. The laser heats and melts this to make the appearance of the pits and lands of pre-recorded CDs. CD-RW discs can be re-recorded on up to 1,000 times, but must be blanked in between recordings. They can be read many times. Due to file systems used for re-writing the discs, storage capacity is usually less than 640 MB.

DVD 类型

Types of DVDs

与简单的单面 CD 不同，DVD 有单面、单层光盘 (SS SL)；单面双层圆盘 (SS DL)；双面单层光盘 (DS SL) 和双面双层光盘 (DS DL)。单层 DVD 的存储容量为 4.7 GB，而双层 DVD 可存储多达 8.5 GB 的数据。使用 MPEG-2 压缩的 8.5 GB DVD 最多可容纳四个小时的标准清晰度视频。用于 DVD 的 MPEG-2 压缩过程通常建立在 40:1 的压缩比之上。由于容量更大，DVD 通常用于录制动态图像，例如电影、游戏和交互式视频。

Unlike the simple single-sided CD, DVDs are available as single-sided, single-layered discs (SS SL); single-sided, double-layered discs (SS DL); double-sided, single layered discs (DS SL) and double-sided, double layered discs (DS DL). Single-layered DVDs have a storage capacity of 4.7 GB, while double-layered DVDs can store as much as 8.5 GB of data. An 8.5 GB DVD can hold up to four hours of standard definition video using MPEG-2 compression. The MPEG-2 compression process used for DVDs is generally built on a 40:1 compression ratio. DVDs, because of their greater capacity, are often used for recording images in motion, such as movies, games and interactive video.

图 20.4 DVD 层的类型

Figure 20.4 Types of DVD Layers

DVD 的每一面都可以包含两层数据。最接近表面的层被烧制在透明涂层上，使激光可以改变焦点并读取其后面层的信息（图 20.4）。DVD 的两面都可以有这两层，但这意味着用户必须将 DVD 翻转过来。一些发行的电影每一面都有不同的电影格式——一侧 16 × 9，另一侧 4 × 3。

Each side of a DVD can contain two layers of data. The layer closest to the surface is burned on a transparent coating that allows the laser to change focus and read the information of the layer behind it (Figure 20.4). It is possible to have these two layers on both sides of a DVD, but it means that the DVD must be flipped over by the user. Some movies were released that had different formats of the movie on each side—16 × 9 on one side and 4 × 3 on the other.

DVD-ROM（DVD-只读存储器）：这些光盘的制作方式与 CD-ROM 类似。它们是使用母盘压制的。这些光盘可以是单面单层 (DVD-5)、单面双层 (DVD-9)，或者很少有双面单层或双面双层。

DVD-ROM (DVD–Read-Only Memory): These discs are produced in a similar fashion to CD-ROMs. They are pressed using master discs. These discs can be single-sided and single-layer (DVD-5), single-sided and double-layer (DVD-9), or, rarely, double-sided and single-layer or double-sided and double layer.

DVD-RAM（DVD—Random Access Memory）：DVD-RAM 光盘可重写，主要用于计算机数据记录。它们在使用上最类似于软盘或硬盘驱动器。记录层是结晶金属合金。DVD-RAM 光盘的容量介于 2.58 GB 和 9.4 GB 之间，可以是单面或双面的。

DVD-RAM (DVD—Random Access Memory): DVD-RAM discs are rewritable and used mainly for computer data recording. They are most closely akin to a floppy or hard drive in usage. The recording layer is a crystalline metal alloy. DVD-RAM discs have a capacity between 2.58 GB and 9.4 GB and may be single or double sided.

DVD-R (DVD–Recordable)：DVD-R 和 DVD-R DL（DVD-R 双层，也称为 DVD-10）光盘类似于 CD-R 光盘。DVD-R 的存储容量为 4.7 GB，DVD-R DL 的存储容量为 8.54 GB。更大的存储容量是通过更小的坑尺寸和更窄的轨道实现的。使用波长比用于写入 CD-R 光盘的激光束更短的激光束。这需要使用与用于 CD-R 光盘制造的染料不同的染料。DVD-R 和 DVD-R DL 光盘由两张聚碳酸酯光盘夹在一起制成，其中一张光盘具有反射层、记录染料和轨道。DVD-RW 光盘类似于 CD-RW 光盘。他们在录音级别使用结晶金属合金。

DVD-R (DVD–Recordable): DVD-R and DVD-R DL (DVD-R Double Layer, also known as DVD-10) discs are similar to the CD-R discs. The storage capacity is 4.7 GB for the DVD-R and 8.54 for DVD-R DL. The greater storage capacity is achieved by smaller pit size and a narrower track. A laser beam with a shorter wavelength than that used for writing to CD-R discs is used. This necessitates the use of a different dye than that used for CD-R disc manufacture. DVD-R and DVD-R DL discs are made with two polycarbonate discs sandwiched together, with one disc having the reflecting layer, recording dye and track. DVD-RW discs are similar to CD-RW discs. They utilize a crystalline metal alloy in the recording level.

蓝光光盘 (BD)

Blu-ray Disc (BD)

光学介质可能看起来与人眼相似，但 CD、DVD 和蓝光光盘在技术上存在重要差异。例如，CD 和 DVD 播放器和刻录机使用红色激光束，而蓝光技术使用波长更小的蓝紫色激光束。由于占地面积较小，与波长较长的激光相比，激光可以在相同尺寸的光盘上读取和记录更多的内容。CD 使用红外线 780 nm（微米）波长的激光束，DVD 使用 650 nm，Blu-ray 的蓝紫色激光束使用波长 405 nm（图 20.5（图 25））。

Optical media may look similar to the human eye, but CDs, DVDs, and Blu-ray Discs have important technological differences. For example, CD and DVD players and recorders use red laser beams, while Blu-ray technology employs a blue-violet laser beam, which has a much smaller wavelength. With a smaller footprint, the laser can read and record much more content on the same size disc than a laser with a bigger wavelength. CDs use an infrared 780 nm (microns) wavelength laser beam, DVDs use a 650 nm, and Blu-ray’s blue-violet laser beam uses a wavelength of 405 nm (Figure 20.5 (Plate 25)).

由于激光光束的频率更高、波长更短，蓝光光盘的存储容量从 25 GB 不等 单面光盘为 50 GB 双面光盘。与 DVD 一样，蓝光可用于存储数据文件或视频内容。由于其更大的数据存储能力，高清项目通常以蓝光光盘的形式发布。可以使用 MPEG 或 H.264 压缩高清视频文件。

Because of the higher frequency and shorter wavelength of the laser’s beam, Blu-ray Disc storage capacities range from 25 GB for a single-sided disc to 50 GB for a double-sided disc. Like DVD, Blu-ray can be used to store either data files or video content. High Definition projects are most often distributed on Blu-ray due to its greater data storage capability. HD video files can be compressed using MPEG or H.264.

图 20.5（图 25） CD、DVD 和蓝光激光束覆盖范围

Figure 20.5 (Plate 25) CD, DVD, and Blu-ray Laser Beam coverage

固态记录格式

Solid State Recording Formats

虽然一些用于专业设置（例如工作室和远程制作）的摄像机本身不进行录制，但大多数普通摄像机都能够将图像捕捉到可移动介质中。这些“摄像机”中的第一台使用录像带。随着其他媒体的出现，制造商将改进格式。有些相机使用光学介质；然而，大多数系统都是基于固态记录的。

While some cameras used in professional settings, such as studios and remote productions, do not make recordings themselves, most common cameras have the ability to capture images to removable medium. The first of these “camcorders” worked with video tape. As other media became available, manufactures incorporated the improved formats. Some cameras use optical media; however, the majority of systems are based on solid-state recording.

固态记录介质源于计算机使用的称为 EEPROM 或电可擦除可编程只读存储器的技术。有时称为闪存，这是一种计算机存储器，即使在电路断电时也能保持其重新编码状态。它可以多次擦除和重新记录。最初，这种类型的存储器对于记录视频信号中的大量数据来说速度太慢且成本太高。但是，随着其他计算机的进步，每字节存储的价格随着时间的推移而降低。结合相机数据压缩，这是现在相机的主要记录媒体。

Solid-state recording media grew from the technology used by computers called EEPROM, or Electrically Erasable Programmable Read-Only Memory. Sometimes called flash memory, this is a form of computer memory that maintains its recoded state even when there is no power to the circuit. It can be erased and re-recorded many times. Initially this type of memory was too slow and too expensive for recording the massive amount of data in a video signal. But, as with other computer advances, the prices per byte of storage have diminished with the passing of time. Combined with on-camera data compression, this is now the predominant recording medium for cameras.

图 20.6 松下 P2 存储卡

Figure 20.6 Panasonic P2 Memory Card

记录媒体或卡有许多不同的形状因素。有些，如松下 P2 卡或索尼 SxS 卡，是制造商与相机规格相匹配的专有格式（图 20.6）。其他，例如 SD（安全数字）卡， 可用于范围更广的静态和摄像机、录音机、计算机和电话。闪存的另一种形式是 USB 记忆棒。

The recording media, or cards, come in many different form factors. Some, such as the Panasonic P2 cards or Sony SxS cards, are proprietary formats matched by the manufactures to the specifications of the camera (Figure 20.6). Others, such as SD (secure digital) cards, are useable by a broader range of still and video cameras, audio recorders, computers and phones. Another form of flash memory is the USB memory stick.

一些高端相机使用的另一种形式是 SSD，即固态驱动器。这本质上是使用磁盘驱动器上的接口类型的大容量固态存储器。这是非常快的内存，高端相机使用它来记录未压缩的视频。这些驱动器也可用于笔记本电脑和台式电脑。虽然比“旋转”磁盘更昂贵，但它们更坚固并且提供更快的数据访问。

Yet another form used by some high-end cameras is the SSD, or solid-state drive. This is essentially high capacity solid-state memory using the kind of interface found on magnetic disk drives. This is very fast memory and is used by high-end cameras to record uncompressed video. These drives are also available for laptop and desktop computers. While more expensive than “spinning” magnetic disks, they are more robust and offer much faster data access.

磁记录

Magnetic Recording

今天，大多数磁记录都发生在计算机磁盘驱动器上，但磁带记录的基本技术可以追溯到第二次世界大战。Ampex 公司在 1940 年代首次将其商业化用于音频。在 20 世纪 50 年代中期，第一台磁带录像机或 VTR 被引入，使用 Ampex VR1000 进行延时编程。到 20 世纪 80 年代，录制的信号开始从模拟过渡到数字。到 20 世纪 90 年代后期，廉价计算机磁盘的可用性使我们今天熟悉的那种基于文件的记录成为可能。

Today, most magnetic recording takes place on computer disk drives, but the basic technology for magnetic tape recording dates back to the Second World War. Ampex Corporation first commercialized it for audio in the 1940s. In the mid 1950s, the first video tape recorders, or VTRs, were introduced for time delay programming using the Ampex VR1000. By the 1980s, the recorded signal began to transition from analog to digital. The availability of inexpensive computer disks by the late 1990s made possible the kind of file-based recording we are familiar with today.

磁介质是基于电信号通过导线并在周围 产生磁场的物理原理 电线。如果那根电线缠绕在一个软铁芯上，那个铁芯就会变成一个电磁铁（图 20.7）。该过程可以逆转。在线圈中移动的磁化铁芯可用于在线圈中产生电流。

Magnetic media is based on the physics principle that electrical signals pass through a wire and create a magnetic field around the wire. If that wire is wrapped around a soft iron core, that iron core will become an electromagnet (Figure 20.7). The process can be reversed. A magnetized iron core moving in a coil of wire can be used to create an electrical current in the coil of wire.

图 20.7 铁芯周围的线圈

Figure 20.7 Coils of Wire Around an Iron Core

在磁带录音机等磁记录设备上，有一个记录头，它是机器记录信号的部分（图 20.8）。这个唱片头包含一个缠绕在软铁芯上的线圈。视频或声音信号被转换为电能。当这种电能流过唱片磁头中的线圈时，它会使唱片磁头变成一块磁铁。磁场的强度取决于流过它周围的线圈的电量。

On a magnetic recording device, such as a videotape recorder, there is a record head, which is the part of the machine that records the signal (Figure 20.8). This record head contains a coil of wire wrapped around a soft core of iron. The video or sound signals are converted to electrical energy. When this electrical energy flows through the coil of wire in the record head, it causes the record head to become a magnet. The strength of the magnetic field varies depending on the amount of electricity that is flowing through the coil of wire around it.

铁芯弯曲成两端不接触的圆形。将两端接触在一起将完成能量流，铁芯不能用于磁化磁带或磁盘。因此，在两极之间留有间隙或空间。这个间隙是一个小开口，在高倍放大下是可见的。 通过留下这个间隙，磁能流沿着阻力最小的路径流动，即到达记录表面。表面上的涂层具有更大的磁导率，因此提供了比试图穿过磁铁两端之间的间隙更容易的路径。磁能自行沉积并储存在那里。

The iron core is bent in the shape of a circle where the ends do not touch. Touching both ends together would complete the energy flow and the iron core could not be used to magnetize the tape or disk. Therefore, a gap or space is left between the two poles. This gap is a small opening that is visible under high magnification. By leaving this gap, the flow of magnetic energy follows the path of least resistance, which is to the recording surface. The coating on the surface has greater permeability and therefore provides an easier path than trying to cross the gap between the two ends of the magnet. The magnetic energy deposits itself and is stored there.

图 20.8 视频磁头

Figure 20.8 Video Heads

当磁带或磁盘通过磁头时，不同的磁能水平（称为通量）磁化表面上的粒子。电量和磁能随信号强度而变化。在模拟记录中，信号代表所记录数据的振幅和频率。磁能水平类似于信号的变化。磁带上的粒子不动。相反，这些小金属颗粒充当小磁铁。作为磁铁，它们会保留其磁能，直到它们通过擦除而消磁或通过用新记录的材料替换信息而改变为止。在数字记录中，磁场的存在或不存在代表正在记录的数据位。

As the tape or disk passes across the head, the varying magnetic energy levels, called flux, magnetize the particles on the surface. The amount of electricity, and thus the magnetic energy, varies depending on the strength of the signal. In an analog recording, the signal represents both the amplitude and frequency of the data being recorded. The levels of magnetic energy are analogous to the variations in the signal. The particles on the tape do not move. Instead, these little particles of metal act as small magnets. As magnets, they retain their magnetic energy until they are either demagnetized through erasure or are altered by replacing the information with newly recorded material. In a digital recording, the presence or absence of a magnetic field represents the bits of data being recorded.

回放录音是相反的过程。被磁化的媒体通过播放头，机器的那部分将磁能转换回电能。变化的磁能水平导致电流在缠绕在回放磁头中的软铁芯周围的线圈中流动。根据磁能的强度，在线圈中产生不同程度的电能。然后将这种电能放大并再现为最初记录的信息。

Playing back the recording is the reverse process. The media, which is magnetized, is passed across the playback head, that part of the machine that converts the magnetic energy back to electrical energy. The varying magnetic energy levels cause electrical current to flow in the coil of wire that is wrapped around the soft iron core in the playback head. Varying levels of electrical energy, based on the strength of the magnetic energy, are produced in the coil of wire. This electrical energy is then amplified and reproduced as the information that was originally recorded.

控制轨道

Control Track

当视频信号被记录到磁带上时，会记录一条控制轨道（图 20.9）。控制轨道的作用类似于电影中的穿孔。如果不是因为电影中的穿孔，就无法将框架放置在放映机门中的正确位置。控制轨道对齐 VTR 中的扫描仪，以便播放从起点开始并在数据轨道的末尾结束。扫描仪或录音/播放头在播放时一次一个地与曲目对齐。

When a video signal is recorded onto magnetic tape, a control track is recorded (Figure 20.9). A control track serves a similar function to perforations in film. If it were not for the perforations in film, there would be no way to place the frame in its proper position in the gate of a projector. The control track aligns the scanner in the VTR so that the playback begins at the start point and finishes at the end of the data track. The scanner or record/playback head aligns itself with the tracks one at a time as it plays them back.

图 20.9 1 英寸录像带轨道

Figure 20.9 1-Inch Videotape Tracks

磁盘记录也有一个结构来对齐和定位记录文件的位置。在磁盘的情况下，表面排列在轨道和扇区中。这些是在格式化磁盘时创建的。硬盘驱动器也有多个盘片或表面，每个盘片或表面都有自己的磁头组件。这既增加了磁盘的容量，又使访问文件的速度更快。盘片、磁道和扇区的大小和数量因磁盘驱动器型号而异。

Magnetic disk recordings also have a structure to align and locate the position of the recorded files. In the case of disks, the surface is arranged in tracks and sectors. These are created when the disk is formatted. Hard drives also have multiple platters, or surfaces, each with its own head assembly. This both increases the capacity of the disk and makes accessing the files faster. The size and number of platters, tracks and sectors vary by disk drive model.

硬盘驱动器和 RAID 系统

Hard Drives and RAID Systems

数字数据在转换为磁能后可以记录在硬盘上。硬盘驱动器是另一种由钢制成的磁盘存储设备，其上记录了数字数据。记录通过记录头进行，其结构和类型类似于基于磁带的记录设备。唱片磁头由包裹在线圈中的软铁芯组成。它安装在一个可移动的机械臂上，允许磁头在不接触磁盘表面的情况下靠近。当磁盘高速旋转时，记录磁头会在磁盘上标记为可用空间的任何部分上磁化磁盘表面。当手臂上下移动将数据存放在磁盘上时，它会发出咔哒声。

Digital data, when converted to magnetic energy, can be recorded on a hard drive. A hard drive is another type of magnetic disk storage device made of steel onto which the digital data is recorded. Recording occurs through a record head, similar in construction and type to a tape-based recording device. The record head consists of a soft iron core enclosed in a coil of wire. It is mounted on a movable mechanical arm that allows the head to be brought into close proximity without touching the disk surface. As the disk rotates at high speed, the record head magnetizes the disk surface on whatever part of the disk is flagged as available space. As the arm moves up and down depositing data on the disk, it emits an audible clicking noise.

硬盘驱动器可以是内置的，安装在计算机内，也可以是便携式的，例如通过电缆连接到计算机的 USB 或 FireWire 硬盘驱动器。磁盘驱动器是使用高速旋转部件的机械设备，经常发生故障。通过将驱动器组合在一起，可以在多个磁盘上复制数据。分组还允许比单个驱动器更多的存储，并且可以安排以减少记录和再现文件所需的时间。这种类型的冗余称为RAID系统，独立磁盘冗余阵列 （图 20.10）。RAID 可以包含任意数量的驱动器，但至少需要两个驱动器协同工作。

Hard drives can be internal, mounted inside a computer, or portable such as in the case of USB or FireWire hard drives that attach to computers through a cable. Disk drives are mechanical devices using high-speed spinning components, and frequently fail. By grouping drives together, data can be duplicated on more than one disk. Grouping also allows for more storage than a single drive, and can be arranged to decrease the amount of time it takes to record and reproduce files. This type of redundancy is referred to as a RAID system, a Redundant Array of Independent Disks (Figure 20.10). A RAID may consist of any number of drives, but requires at least two drives working together.

图 20.10 RAID 阵列

Figure 20.10 RAID Array

RAID 有多种级别，例如 RAID 0、RAID 1、RAID 5 等，每种级别都采用不同的组织或策略来跨硬盘驱动器分配数据。每个 RAID 级别都有自己的优势，其中可能包括增加的存储容量、卓越的数据完整性、更好的容错能力和更快的吞吐量性能。不同的级别通过在有效使用方面受到不同的惩罚来实现这些好处存储空间、数据读/写速度和不同的容错性能。

There is a variety of levels of RAID, such as RAID 0, RAID 1, RAID 5, and so on, each one employing a distinct organization or strategy in the distribution of the data across the hard drives. Each RAID level offers its own benefits, which might include increased storage capacity, superior data integrity, better fault tolerances, and faster throughput performance. The different levels achieve these benefits with varying penalties being exacted with regard to efficient use of storage space, speed of data read/write, and varying fault tolerance performances.

RAID 系统中使用的数据组织策略是：

The strategies of data organization utilized in RAID systems are:

条带化：数据以条带形式写入阵列中的磁盘，每个条带由相同数量的数据组成，可以是字节级的，也可以是块级的，并按顺序写入磁盘：磁盘 1，磁盘 2，然后放置磁盘 1 上的下一个条带，依此类推。条带化减少了数据的访问时间，因为读/写操作是在阵列中的所有硬盘驱动器上同时执行的，而不是从一个驱动器访问数据。

Striping: The data is written across the disks in the array in stripes, each stripe consisting of the same amount of data, either at the byte-level or in blocks, and written across the disks sequentially: disk 1, disk 2, then laying the next stripe on disk 1 again, and so on. Striping decreases the access times for data, as read/write operations are performed on all hard drives in the array at once, rather than the data being accessed from one drive.

镜像：数据以块为单位写入，块在磁盘上进行镜像：磁盘 1 中的块被镜像到磁盘 2 上，磁盘 1 上的块在磁盘中按顺序排列。

Mirroring: The data is written in blocks, with the blocks being mirrored across the disks: blocks in disk 1 being mirrored on disk 2, the blocks on disk 1 being laid out sequentially through the disk.

双工：双工本质上类似于镜像，只是要双工的每个磁盘（或磁盘组）都有自己的硬件控制器。就存储容量而言，镜像和双工是效率最低的 RAID 策略，因为有效存储是 RAID 硬盘驱动器总实际容量的一半。然而，镜像和双工提供了完全的数据冗余，并在硬盘驱动器发生故障时提供了最快的恢复丢失数据的可能。

Duplexing: Duplexing is essentially like mirroring, only each disk (or set of disks) to be duplexed has its own hardware controller. Mirroring and duplexing are the most inefficient RAID strategies in terms of storage capacity as the effective storage is half the actual capacity of the total on the RAID hard drives. However, mirroring and duplexing provide a complete redundancy of data and provide for the fastest possible recovery of lost data in the event of a hard drive failure.

奇偶校验：计算世界中的奇偶校验是一种对一组二进制数据进行检查的功能，例如通过标记它是否具有偶数或奇数。此奇偶校验数据存储在整个 RAID 阵列中。奇偶校验可在硬盘驱动器发生故障时防止数据丢失，而不会因有效存储容量损失而产生高额开销。如果使用软件 RAID 控制器，在故障硬盘驱动器上恢复数据的成本需要高性能CPU 执行必要的计算以重建丢失的数据。

Parity: Parity in the computing world is a function that provides a check on a set of binary data, for example by notating if it has an even or odd number of ones. This parity data is stored across the RAID array. Parity protects against the loss of data in the event of hard drive failure without the high overhead of effective storage capacity loss. If a software RAID controller is being utilized, the cost of recovering data on a failed hard drive is in the need for a high performance CPU to perform the necessary computations to rebuild the missing data.

RAID 可以通过硬件实现（使用特殊的硬件控制器卡）或通过普通计算机驱动器控制器使用软件来实现。每种实施都有其自身的优势，而某些 RAID 级别仅适用于硬件控制器。

RAID can be achieved by either hardware implementations, using a special hardware controller card, or by use of software through the normal computer drive controllers. Each implementation has its own benefits, while some RAID levels work only with hardware controllers.

RAID 级别

RAID Levels

有许多 RAID 级别在使用中，每一种都有自己的优点和缺点，并且每一种都适用于不同的应用程序。以下是媒体应用程序中最常见的内容。

There are a number of RAID levels in use, each one offering its own advantages and disadvantages, and each one suitable for use in different applications. The following are the ones most commonly seen in media applications.

RAID 0是一种简单的设计，它使用条带阵列允许快速数据访问和最经济地使用硬盘驱动器存储，但不提供容错。如果单个驱动器发生故障，RAID 阵列中的所有数据都会丢失。应用领域包括视频和其他图像制作和编辑，以及任何其他需要高吞吐量的应用。

RAID 0 is a simple design that uses a striped array allowing for fast data access and the most economical use of hard drive storage, but provides no fault tolerance. In the event of a single drive failure, all the data in the RAID array is lost. Areas of application include video and other image production and editing, and any other application requiring high throughput.

RAID 1利用镜像或双工。数据在一个驱动器中按顺序放置，并成对镜像。这提供了所有数据的完整副本，但在磁盘空间消耗方面效率低下。RAID 1 用于需要高可用性的应用程序，例如金融机构。

RAID 1 utilizes mirroring or duplexing. The data is laid down sequentially within one drive, and mirrored in its pair. This provides a complete copy of all data but is inefficient with regard to disk space consumed. RAID 1 is used in applications requiring high availability such as at a financial institution.

RAID 3使用字节级条带化和奇偶校验。奇偶校验记录在专用磁盘上。此级别在存储使用方面非常高效，并提供高数据传输速率。RAID 3 通常通过使用硬件控制器来实现。它的应用包括视频制作；需要高数据吞吐量的视频直播、图像和视频编辑。RAID 3 组中的任何一个驱动器都可以发生故障而不会丢失数据。可以更换损坏的单元并恢复 RAID 集。如果两个或更多驱动器发生故障，则整个数据集都会丢失。

RAID 3 uses byte-level striping and parity. The parity is recorded on a dedicated disk. This level is highly efficient in storage usage and provides high data transfer rates. RAID 3 is usually achieved by use of a hardware controller. Its applications include video production; live streaming of video, image and video editing, which require high data throughput. Any one drive in a RAID 3 set can fail without loss of data. The bad unit can be replaced and the RAID set restored. If two or more drives fail, the entire data set is lost.

RAID 5在字节级别使用数据条带化，奇偶校验在可用驱动器之间条带化。这种策略提供了高性能和良好的容错能力。RAID 5 是最流行的 RAID 实现。应用程序包括服务器，无论是用于文件、数据库、Web、电子邮件还是 Intranet。与 RAID 3 一样，可以容忍任何单个驱动器故障并恢复 RAID。

RAID 5 uses data striping at the byte level, parity being striped across the available drives. This strategy provides high performance and good fault tolerance. RAID 5 is the most popular implementation of RAID. Applications include servers, whether being used for files, databases, web, email or intranet. Like RAID 3 any single drive failure can be tolerated and the RAID restored.

RAID 6类似于 RAID 5，仅使用块级条带化和两种奇偶校验方案，提供更高的容错能力。它的用途类似于 RAID 5。通过创建第二级奇偶校验，最多两个驱动器可能会发生故障而不会丢失数据。然而，这种额外的保护是以为奇偶校验数据保留两倍于 RAID 级别 3 和 5 的空间为代价的。

RAID 6 is similar to RAID 5 only using block level striping and two parity schemes, providing greater fault tolerances. Its uses are similar to those of RAID 5. By creating a second level of parity, up to two drives may fail without the loss of data. However, this extra protection comes at the cost of reserving twice as much space as RAID levels 3 and 5 for parity data.

其他 RAID 格式结合了上述基本思想。

Other RAID formats combine the basic ideas above in combination.

RAID 0 + 1采用 RAID 0 条带阵列，然后将其镜像为 RAID 1 阵列。这方面的应用包括对高性能的需求，而不需要最高的可靠性。

RAID 0 + 1 employs RAID 0 striped arrays which are then mirrored as RAID 1 arrays. Applications for this would include a need for high performance without the need for the highest reliability.

RAID 10使用条带化和镜像来实现其可靠性和性能。本质上，它由 RAID 1 阵列组成，然后像 RAID 0 一样进行条带化。此应用程序是需要 RAID 0 的高吞吐量和 RAID 1 提供的高容错能力的数据库服务器。它的效率非常低它使用存储，每个 RAID 1 段至少需要两个驱动器。

RAID 10 uses striping and mirroring to achieve its reliability and performance. In essence it is comprised of RAID 1 arrays that are then striped as in RAID 0. The applications for this are database servers with a need for the high throughput of RAID 0 and the high fault tolerances provided by RAID 1. It is very inefficient in its use of storage, requiring a minimum of two drives for each RAID 1 segment.

RAID 30是 RAID 3 和 RAID 0 的组合。虽然价格昂贵，但它提供了极高水平的吞吐量和容错能力。

RAID 30 is a combination of RAID 3 and RAID 0. While expensive, it offers extremely high levels of throughput and fault tolerance.

RAID 50是通过 RAID 0 条带化和 RAID 5 奇偶校验实现的组合实现的。它适用于需要 RAID 5 优势但具有额外吞吐量的应用程序。

RAID 50 is achieved by a combination of RAID 0 striping and RAID 5 parity implementations. It is appropriate in applications that need the benefits of RAID 5 but with additional throughput.

还有其他几种 RAID 组合变体用于满足数据处理中的特定需求。这些组合的详细信息可以在许多特定于其应用程序的不同来源中找到，例如图书馆、硬件制造商以及金融和教育机构。

There are several other variations of RAID combinations used to serve specific needs in data handling. Details of these combinations can be found at a number of different sources specific to its application such as libraries, hardware manufacturers and financial and educational institutions.

正如您在本书中了解到的那样，虽然有许多录制和存储视频资料的选项，但技术正在以非常快的速度变化。但是新技术通常是从当前使用的格式和设备中产生的。因此，通过了解技术如何发展到今天的状态，以及当今视频世界的各种用途，您将为理解未来的技术打下良好的基础。

While there are many options to record and store video material, as you have learned throughout this book, technology is changing at a very rapid rate. But new technology typically grows out of the formats and devices that are currently in use. So by learning how technology has progressed to where we are today, and the variety of uses in today’s video world, you will create an excellent foundation for understanding the technology of tomorrow.

什么是流媒体？

What is Streaming Media?

在本章的后面，您将了解广播电视如何利用流视频。但首先，让我们后退几步，看看什么是流媒体以及它如何成为视频世界的重要组成部分。

Later in this chapter, you will learn how broadcast television utilizes streaming video. But first, let’s take a few steps back and look at what streaming is and how it has become such an important part of the video world.

图 21.1在移动设备上播放电影

Figure 21.1 Streaming a Movie on a Mobile Device

流式传输是通过 Internet 将媒体作为压缩形式的连续数据流传送的过程。当媒体开始到达时，它会实时显示在查看设备上，但不会保存到设备的硬盘驱动器中。要查看媒体，最终用户需要一个称为播放器的特殊软件来解码或解压缩数据，将视频发送到设备的屏幕，将音频发送到设备的扬声器（图 21.1）。播放器可以从特定软件制造商的网站下载，也可以是浏览器（如 Internet Explorer、Safari、Chrome 或 Firefox）的组成部分，或者是联网设备的一部分。

Streaming is the process of delivering media over the Internet as a continuous stream of data in a compressed form. As the media begins to arrive, it is displayed on a viewing device in real time, but it is not saved to the device’s hard drive. To view the media, the end user needs a special piece of software called a player that decodes or un-compresses the data sending the video to the device’s screen and audio to the device’s speakers (Figure 21.1). Players can either be downloaded from a particular software maker’s Web site, or they can be an integral part of a browser such as Internet Explorer, Safari, Chrome or Firefox, or part of an Internet-connected device.

流媒体对观众和内容交付者都有一些非常明显的优势。观众可以执行自定义的视频搜索并创建播放列表。内容交付者能够收集有关访问者正在观看的内容以及观看时长的数据。他们可以更有效地利用带宽，因为观众无需先完全下载就可以开始观看电影或媒体。内容创建者也受益，因为他们对自己的知识产权拥有更大的控制权。一旦播放视频数据，它就会被媒体播放器丢弃，并且不会存储在观众的计算机上。

Streaming media has some very distinct advantages for both viewers and content deliverers. Viewers can perform customized searches for videos and create playlists. Content deliverers are able to collect data on what visitors are watching and for how long. They can utilize bandwidth more efficiently because the viewer can begin watching the movie or media without it being fully downloaded first. The content creator also benefits because they have far greater control over their intellectual property. Once the video data is played, it is discarded by the media player and not stored on the viewer’s computer.

流媒体的历史

The History of Streaming Media

在当今世界，随着互联网的普及，消费者认为音频和视频流是理所当然的。但是流媒体是从哪里开始的呢？流媒体实际上可能早在 1920 年就开始了，当时陆军少将 George O. Squier 完善了一项技术，可以在不使用无线电的情况下向商业客户流式传输连续音乐。他通过电线传输音乐来做到这一点。这项技术促成了他的公司 Muzak 的发展，这导致了今天所谓的电梯音乐。由于收音机也在同一时间出现，将军不得不为他的技术寻找其他用途，例如为商店、餐馆和办公楼的电梯提供背景音乐，因此提到了“管道输入”电梯音乐.

In today’s world, consumers take audio and video streaming for granted as access to the Internet is now pervasive. But where did streaming begin? Streaming media may have actually gotten its start as early as 1920 when Army Major General George O. Squier perfected a technology for streaming continuous music to commercial customers without the use of radio. He did this by transmitting music across electrical wires. This technology led to the development of his company, Muzak, which led to what is referred to today as elevator music. Since radio was also on the horizon at the same time, the General had to find other uses for his technology, such as providing background music for stores, restaurants, and elevators in office buildings, thus the reference to “piped-in” elevator music.

时间快进到 1993 年，当时科学家们为了证明他们的新多播技术行之有效，在互联网上播放了乐队的表演 Severe Tire Damage。1994 年，滚石乐队在互联网上播放了他们的一场巡回演唱会。然而，图像很小，大约 1.5 × 1.5 英寸，无法全速显示，每秒只有 1-10 帧左右。其他流媒体事件不断涌现，1995 年，一家名为 RealNetwork Inc.（当时称为 Progressive Networks）的新公司提供了纽约洋基队和西雅图水手队之间棒球比赛的互联网音频广播。这成为音频流历史上的决定性时刻。1997年，RealNetwork推出流媒体视频技术。

Fast forward to 1993, when scientists, wanting to prove their new multicasting technology worked, broadcast a performance by the band, Severe Tire Damage, over the Internet. In 1994, the Rolling Stones broadcast one of their concert tours on the Internet. The image, however, was quite small, about 1.5 × 1.5 inches, and could not be displayed at full speed, only about 1–10 frames per second. Other streaming events trickled out and in 1995, a new company by the name of RealNetwork Inc. (called Progressive Networks at the time) provided an Internet audio broadcast of a baseball game between the New York Yankees and the Seattle Mariners. This became a defining moment in audio streaming history. In 1997, RealNetwork launched streaming video technology.

到 2000 年，RealNetwork 成为强大的流媒体内容提供商，占互联网流媒体内容的 85% 以上。RealNetwork 通过为使用 Windows 操作系统的 PC 提供免费的音频/视频 Real 播放器，在短短三年内完成了这一壮举。与此同时，微软开始看到拥有自己的播放器的优势。

By the year 2000, RealNetwork became a powerhouse streaming content provider accounting for more than 85% of the Internet’s streaming content. RealNetwork accomplished this feat in three short years by providing a free audio/video Real player for PCs using the Windows operating system. At the same time, Microsoft started seeing the advantage of having its own player.

尽管 Real 播放器是免费的，但它的市场份额开始被微软夺走。消费者开始反对第三方 Real Player 将自己设为所有多媒体内容的默认播放器，以及安装时的多个后台进程和升级消息弹出窗口。它很快就失去了吸引力，几乎在一夜之间从必不可少的角色变成了被消费者抛弃。

Although the Real player was free, it began to lose its marketplace share to Microsoft. Consumers started objecting to the third party Real player making itself the default player for all multimedia content, as well as the multiple background processes upon installation and the message pop-ups to upgrade. It soon lost its appeal and went from being the essential player to being dropped by the consumer virtually overnight.

微软时代

The Microsoft Era

从 2000 年到 2007 年，微软主导了计算机市场。Windows Media Player 占据了个人计算市场的最大份额，因此跃居前列，这使其成为 Internet 以及大多数公司内部网上使用最广泛的多媒体传输格式。该播放器不可定制，需要第三方插件才能在 Mac 上播放，而 Mac 的市场份额要小得多。

From 2000 to 2007, Microsoft dominated the computer marketplace. Having the lion’s share of the personal computing market vaulted the Windows Media Player to the forefront, which made it the most widely used multimedia delivery format on the Internet as well as most company’s intranets. The player was non-customizable and it required a third party plug-in that enabled it to play on a Mac, which had a much smaller share of the market.

在同一时期，HTML（超文本标记语言）——互联网语言——面临着一种名为Flash的新语言的挑战。Flash 的美妙之处在于它具有更大的设计灵活，并且比 HTML 更具交互性。尽管 Flash 有一个视频组件，但它的性能并不好，而且提供的视频和音频质量很差，而且存在同步问题。2005 年，Flash 的发明者 Macromedia 从 On2 Technologies 获得了一种名为 VP6 的视频压缩编解码器的许可。这种新的编解码器极大地改进了 Flash 的音频/视频同步，使 Macromedia 可以与微软竞争。

During the same time period, HTML (Hyper Text Markup Language)—the language of the Internet—was facing a challenge from a new language called Flash. The beauty of Flash was that it had greater design flexibility and was far more interactive than HTML. Although Flash had a video component, it was not a good performer and offered poor quality video and audio with sync issues. In 2005, the inventors of Flash, Macromedia, licensed a video compression codec called VP6 from On2 Technologies. This new codec greatly improved the audio/video synchronizations of Flash allowing Macromedia to give Microsoft a run for their money.

闪电时代

The Flash Era

在 Macromedia 获得 VP6 技术许可后不久，其竞争对手 Adob​​e 收购了 Macromedia。Adobe 随后启用他们的 Flash Player 以匹配 Microsoft 品牌播放器的视频质量，从而允许完全集成到基于 Flash 的站点中。这个游戏规则改变者使 Flash 成为真正的跨平台交付系统，成为当时最流行的流媒体技术。

Shortly after Macromedia licensed the VP6 technology, its rival, Adobe, purchased Macromedia. Adobe then enabled their Flash Player to match the video quality of Microsoft’s brandable player allowing for full integration into Flash-based sites. This game changer made Flash a truly cross platform delivery system that became the most prevalent streaming technology of the day.

2007 年，Microsoft 试图与他们称为 Silverlight 的 Flash 竞争对手抗衡，但那时大多数娱乐和广播网站都对 Flash 进行了大量投资。Silverlight 从未达到微软所希望的市场渗透率，它们在这些市场中的份额在 2010 年下降到个位数。

In 2007, Microsoft tried to counter with a Flash competitor they called Silverlight, but by then most of the entertainment and broadcast sites were heavily invested in Flash. Silverlight never achieved the market penetration Microsoft had hoped for and their share in these markets decreased to single digits in 2010.

2010 年 4 月，当微软的数量在下降时，苹果推出了不支持 Flash 的 iPad。相反，Apple iOS 设备上的视频播放技术是 HTML5，一种旧网络语言的最新更新版本。Apple 再次改变了竞争环境，因为与基于插件的 Flash、Windows Media 或 Silverlight 技术不同，HTML5 使用浏览器的本地播放器来播放来自 YouTube 等网站的嵌入式视频和音频文件。

In April, 2010, while Microsoft’s numbers were declining, Apple introduced the iPad, which had no support for Flash. Instead, the video playback technology on Apple’s iOS devices was HTML5, a newly updated version of the old web language. Apple changed the playing field yet again because unlike the plug-in based technologies of Flash, Windows Media or Silverlight, HTML5 uses a browser’s native player to play back embedded video and audio files from websites such as YouTube.

HTML5 视频时代

The HTML5 Video Era

今天有许多语言用于创建网站，但 HTML（超文本标记语言）是这一切的开始。最新版本的 HTML5 具有许多优势，可使交付多媒体（也称为富内容）变得更加简单。观众不再需要下载插件来观看 YouTube 视频或收听流媒体音乐。

Today there are many languages used to create websites, but HTML (Hyper Text Markup Language) was the start of it all. The newest version of HTML5 has many advantages that make delivering multimedia, also called rich content, much simpler. Viewers no longer need to download a plug-in in order to watch a YouTube video or listen to streaming music.

截至 2014 年 10 月，HTML5 已被万维网联盟 (W3C) 接受为互联网的核心语言。它弥合了计算机和移动设备之间的差距，以在任何设备上提供一致的用户体验。随着越来越多的用户离开他们的桌面并拥抱和依赖移动网络，HTML5 的诸多优势将使公司有机会使用任何 HTML5 兼容的浏览器创建新的、令人兴奋的交互式在线体验。

As of October, 2014, HTML5 has been accepted by the World Wide Web Consortium (W3C) as the core language of the Internet. It bridges the gap between computers and mobile devices to provide a consistent user experience across any device. As more users move away from their desktops and embrace and rely on the mobile Web, the many benefits of HTML5 will give companies the opportunity to create new and exciting interactive online experiences using any HTML5 compatible browser.

图 21.2 代码中的 HTML5 媒体元素

Figure 21.2 HTML5 Media Elements in Code

流媒体技术

Streaming Technologies

Apple 的 QuickTime、Adobe 的 Flash 和 Microsoft 的 Windows Media 和 Silverlight 流技术等应用程序具有某些共同的组件。这些流媒体技术中的每一种都包括在观众设备上播放媒体的播放器、播放器可以播放的一种或多种定义的文件格式以及可以提供实时流媒体或数字版权管理 (DRM) 功能以防止复制的服务器组件，这保护内容所有者的知识产权。

Applications such as Apple’s QuickTime, Adobe’s Flash and Microsoft’s Windows Media and Silverlight streaming technologies have certain components in common. Each of these streaming technologies include a player to play the media on the viewer’s device, a defined file format or formats that the player can play and a server component that may offer live streaming or digital rights management (DRM) features to prevent copying, which protects the content owner’s intellectual property.

所有这些流媒体技术都使用编解码器或视频和音频压缩方案来缩小文件的大小，以便用户可以实时流媒体播放。一些常见的视频压缩编解码器包括 MPEG-4、H.264、VP6 和 VP8、Windows Media Video (WMV)、Google 的 WebM 和 H.265，这是市场上出现的最新视频编解码器。一些常见的音频编解码器包括 AAC（高级音频编码）、Windows Media Audio (WMA) 和 MP3。

All of these streaming technologies use codecs, or video and audio compression schemes, to shrink the size of the files so they can be streamed and played by the user in real time. Some common video compression codecs include MPEG-4, H.264, VP6 and VP8, Windows Media Video (WMV), Google’s WebM and H.265, which is the newest video codec to emerge on the market. Some common audio codecs include AAC (Advanced Audio Coding), Windows Media Audio (WMA) and MP3.

流媒体类型

Streaming Media Types

媒体流可以是直播的，也可以是点播的。实时流或真正的流媒体不会将文件保存到设备的硬盘驱动器。取而代之的是，该文件仅可在活动进行时查看，例如现场直播的体育节目。

Media streams can be either live or on demand. Live streams, or true streaming, does not save the file to the device’s hard drive. Instead, the file is only available to be viewed while the event is in progress, such as a live sports cast.

点播流通常会在硬盘驱动器或服务器上保存较长时间，以便稍后从该位置播放。此方法称为渐进式流式传输或渐进式下载。使用这种渐进式下载方法，用户可以在数据传输完成之前允许访问内容。此外，由于数据保存在用户的硬盘驱动器中，因此流式传输会更加顺畅并且不易受中断影响。直播或点播流媒体有多种类型：

On-demand streams are usually saved to hard drives or servers for extended periods of time to be played back from that location later. This method is referred to as progressive streaming or a progressive download. With this progressive download method, the user is allowed access to the content before the data transfer is complete. Also since the data is saved to the user’s hard drive, it will stream more smoothly and is less susceptible to interruptions. There are several types of live or on-demand streaming:

实时流媒体视频是通过流媒体服务器或专门用于通过特殊服务器传输流媒体的软件程序传输的视频。这不同于传统的网络服务器，后者提供各种形式的网络内容，包括但不限于静止图像、电影文件和 PDF。

Live Streaming Video is video delivered via a streaming server or a software program that is dedicated solely to delivering streaming media through a special server. This differs from a traditional web server that delivers all forms of web content including but not limited to still images, movie files and PDFs.

视频点播(VOD) 是一种交互式电视技术订阅模式，观众可以借此实时观看节目或随时切换到观看预先录制内容库中的存档媒体（图 21.3 ）。

Video on Demand (VOD) is an interactive TV technology subscription model whereby viewers can watch programming in real time or switch to viewing archived media from a library of prerecorded content whenever they want (Figure 21.3).

图 21.3 通过视频点播提供的许多资源

Figure 21.3 Many Sources Available through Video On Demand

Streaming Archive允许观众或听众在提供商的服务器上观看或收听固定时间段内可用的任何节目资料。

Streaming Archive allows viewers or listeners to watch or hear any program material available for a fixed period of time on a provider’s server.

Adaptive Streaming确实是两全其美，尤其是对于带宽较低的移动设备或 Wi-Fi。多个实时或点播流被编码，然后根据设备的连接速度进行切换，因此得名。当连接良好时，例如在具有高速 Internet 连接的功能强大的 PC 上，观众将收到具有高数据速率的高质量信号。但是，如果设备的连接速度下降，视频服务器会检测到速度下降并换档以较低的数据速率传送相同的文件。这样可以使视频信号流在较慢的连接上（例如在移动电话上）保持可接受的质量，希望不会中断。一些自适应流媒体渠道包括 Apple 的 HTTP Live Streaming、Microsoft 的 Smooth Streaming 和 Adob​​e 的 Dynamic Streaming。

Adaptive Streaming is really the best of both worlds, especially for lower bandwidth mobile devices or Wi-Fi. Multiple live or on-demand streams are encoded and then switched based on the device’s connection speed, hence the name. When the connection is good, like on a powerful PC with a high-speed Internet connection, the viewer will receive a high-quality signal with a high data rate. But if the connection speed of the device drops, the video server detects the drop in speed and shifts gears to deliver the same file with a lower data rate. This keeps the video signal streaming at a passable quality on the slower connection, for example on a mobile phone, hopefully without interruption. Some of the adaptive streaming outlets include Apple’s HTTP Live Streaming, Microsoft’s Smooth Streaming and Adobe’s Dynamic Streaming.

Over-The-Top内容 (OTT) 是指通过第三方在线视频租赁网站或订阅服务（如 Netflix、Hulu 或 myTV）在互联网上交付视频和音频内容，无需有线或直接卫星广播参与内容的控制或分发。Internet 服务提供商或 ISP 负责仅将 IP 数据包传输到最终用户的设备。OTT 内容通过联网设备（如计算机、平板电脑和智能手机）或机顶盒（如 Roku、Google TV、智能电视）和许多游戏机（如任天堂的 Xbox 360、索尼 PlayStation 3 和 Wii）使用应用程序访问.

Over-The-Top Content (OTT) refers to the delivery of video and audio content over the Internet by a third party online video rental Web site or subscription service—such as Netflix, Hulu or myTV—without the need for cable or direct satellite broadcast being involved in either the control or distribution of the content. The Internet Service Provider, or ISP, is responsible for transporting only the IP packets of data to the end user’s device. OTT content is accessed using apps through Internet-connected devices such as computers, tablets and smartphones or set-top boxes such as Roku, Google TV, smart TVs and a number of gaming consoles such as Nintendo’s Xbox 360, the Sony PlayStation 3 and Wii.

在线视频分销商( OVD) 是任何分销商，例如 YouTube Insight，它提供由不隶属于 OVD 的个人或公司提供的基于互联网的视频内容。那里有几种服务，只需单击一下，内容创建者就可以将他们的内容传播到许多视频托管服务中。这种批量上传方法节省了内容提供者的时间，还允许他们使用标签和描述来宣传他们的材料。在某些情况下，它甚至可以让提供商通过一个简单的界面来跟踪他们视频的收视率和下载量。

An Online Video Distributor (OVD) is any distributor, for example YouTube Insight, that offers Internet-based video content provided by a person or company that is not affiliated with the OVD. There are several services that with one click allow the content creator to spread their content across a number of video hosting services. This batch upload approach saves the content provider time and also allows them to promote their material with tags and descriptions. In some cases, it may even allow the provider to track the viewership and downloads of their videos with a simple interface.

视频和音频流文件

Video and Audio Streaming Files

您很可能以上述方式之一观看过节目。但是媒体文件本身是如何到达目的地的——你，消费者。假设您访问托管在 Web 服务器上的网页以查找您想要查看或收听的文件。Web 服务器向流媒体服务器发送请求特定文件的消息。Streaming 服务器然后绕过 Web 服务器将文件流式传输到您的计算机。您计算机上的客户端软件解码并播放该文件。相同的过程适用于通过任何设备接收的流媒体。

You have very likely viewed a program in one of the ways described above. But how does the media file itself reach its destination—you, the consumer. Let’s say you visit a web page hosted on a Web server to find a file you want to see or hear. The Web server sends a message to the Streaming media server requesting the specific file. The Streaming server then streams the file to your computer bypassing the Web server. The client software on your computer decodes and plays the file. The same process applies to streaming media received through any device.

虽然流文件体积小且传输效率高，但它通常以较大的高质量文件开始。例如，如果文件来自后期制作，它可能会在 Apple 的 ProRes 或 Avid 的 DNxHD 等母带编解码器中保留编辑系统。从那里开始，它可能已经被压缩到一个中间级别，然后再到达 Web 服务器提供商以压缩成几个版本以供最终交付。

While a streaming file is small in size and efficient to transmit, it usually begins as a larger high-quality file. For example, if the file came from post production, it may have left the edit system in a mastering codec such as Apple’s ProRes or Avid’s DNxHD. From there it may have been compressed to an intermediate level before it went to the web server provider to be compressed in several versions for final delivery.

压缩文件以使其更小的过程丢弃了再现视频或音频不需要的信息。然而，在文件被压缩之前，可以通过降低其分辨率或降低其帧速率来减小其文件大小而不会降低质量。使用这些方法来减少文件压缩前的大小意味着流媒体文件可以更小，压缩后的视频和音频质量更好。

The process of compressing a file to make it smaller throws away information that is not needed to reproduce the video or audio. Before a file is compressed, however, its file size can be reduced without the loss of quality by either making its resolution smaller or by reducing its frame rate. Using these methods to reduce the file size before compression means that the streaming file can be even smaller with a better video and audio quality after compression.

音频流的演变

The Evolution of Audio Streaming

流媒体音频的现状始于 1999 年推出的名为 Napster 的免费点对点 MP3 音频文件互联网下载共享服务。可以说，Napster 是第一个流行的盗版音乐网站。Napster 最初的前提是让音乐爱好者可以轻松地与他们的同龄人分享他们购买的音乐、难以找到的老歌、未发行的录音和音乐会的盗版录音，他们还可以将他们的音乐库上传和下载到中央存储库，并且免费交易音乐。如果你能把它变成一个数字文件并把它放在电脑上，你就可以分享它。不必购买整张专辑，您可以使用 Napster 只获取您想要收藏的歌曲。

The current state of streaming audio had its inauspicious beginnings in a free peer-to-peer MP3 audio file Internet download sharing service called Napster, which launched in 1999. It could be said that Napster was the first popular pirate music site. Napster’s original premise was designed to make it easy for music enthusiasts to share their purchased music, older songs that were hard to find, unreleased recordings and bootleg recordings of concerts with their peers who could also upload and download their musical libraries to a central repository and trade music for free. If you could turn it into a digital file and get it on a computer, you could share it. Instead of having to buy an entire album, you could use Napster to get only the songs you wanted to have in your collection.

虽然这个免费的音乐共享网站是一项技术创新，但它是对没有从这些共享文件中获得收入的唱片艺术家的公然侵犯版权。2000 年 7 月，法院命令迫使 Napster 停止运营。虽然它被确定为非法，但 Napster 分享音乐的新方法非常受欢迎，它迫使音乐行业改变消费者购买音乐的方式。

While this free music-sharing site was a technological innovation, it was a blatant copyright infringement against the recording artists who were not getting revenue from these shared files. In July 2000, a court order forced Napster to cease operations. Although it was determined to be illegal, Napster’s new approach to sharing music was exceedingly popular and it forced the music industry to change the way consumers purchase their music.

输入苹果。2001 年，Apple 推出了他们的媒体播放器 iTunes，该播放器还用作组织音乐的图书馆。不久之后，他们发布了名为 iPod 的便携式媒体播放器系列，两者是绝配。2003 年，Apple 推出了 iTunes 音乐商店，允许消费者以合理的价格从艺术家那里购买整张专辑，或者仅需 99 美分购买单首歌曲。这个游戏规则改变者是 Napster 的合法答案，因为消费者现在重新控制了他们的音乐，音乐行业正在获得收入。

Enter Apple. In 2001, Apple launched their media player, iTunes, which also served as a library to organize music. Shortly after, they released their line of portable media players called iPods, and the two were a perfect match. In 2003, Apple launched the iTunes Music Store, which allowed the consumer to either purchase an entire album from an artist for a reasonable price or purchase a single song for only 99 cents. This game changer was the legal answer to Napster as the consumer was now back in control of their music and the music industry was receiving revenue.

2009 年，Apple 通过其改进的 iTunes Store 再次改变了竞争环境，允许用户将音乐、电视节目、电影、播客、有声读物等下载到智能手机和其他设备。这种集成系统业务模型不仅是媒体播放器和图书馆，而且还是移动设备的管理应用程序。虽然 iTunes 音乐商店最初使用较旧的 MP3 音频文件格式，但在 2004 年，它开始使用更高效的 AAC 音频压缩方案。这有助于节省磁盘空间和电池寿命，同时以低于 MP3 的数据速率获得整体改进的音频文件质量。

In 2009, Apple changed the playing field again with its improved iTunes Store, which allowed users to download music, TV shows, movies, podcasts, audio books, and more to smart phone and other devices. This integrated system business model is not only a media player and library but it is also a management application for mobile devices as well. While the iTunes Music Store originally used the older MP3 audio file format, in 2004, it began to use the more efficient AAC audio compression scheme. This helped save disk space and battery life while getting an improved audio file quality overall at lower data rates than MP3.

在此期间，Napster 仍然活跃在画面中。它已将自己重新设计为拥有大量订阅者的订阅服务。2008 年，电子产品零售商百思买购买了 Napster 的曲库。但是，到 2011 年，百思买将 Napster 卖给了 Rhapsody，这是一家最初由 RealNetwork 拥有的公司。通过此次收购，Rhapsody 成为首个流媒体点播音乐订阅服务，以固定月费提供对超大型数字音乐库的无限下载访问，而不是 Apple iTunes 使用的每首歌曲或专辑购买模式。

During this time, Napster was still in the picture. It had redesigned itself as a subscription service with a healthy number of subscribers. In 2008, the electronics retailer, Best Buy, purchased Napster’s library of songs. But, by 2011, Best Buy had sold Napster to Rhapsody, a company that was originally owned by RealNetwork. With this acquisition, Rhapsody became the first streaming on-demand music subscription service offering unlimited download access to a very large library of digital music for a flat monthly fee instead of the per-song or album purchase model being used by Apple’s iTunes.

在严格的流媒体类别中——即无广告或支持订阅——有 Pandora 网络广播。潘多拉拿东西通过使用称为“音乐基因组计划”的技术进步来提升音频流游戏的方向略有不同，这是一种“特征识别”技术，类似于用于图片中的人脸识别。通过这种方法，在选择下一首歌曲时会考虑超过 450 种不同的音乐属性或“基因”——基因是音乐的特征，例如主唱的性别、律动类型等。Pandora 了解听众的偏好，然后根据他们的偏好过滤目录列表。Pandora 媒体播放器基于名为 OpenLaszlo 的开源应用程序开发平台，可通过任何流媒体设备访问。这里没有下载！

In the strictly streaming category—that is, ad free, or subscription supported—there is Pandora Internet Radio. Pandora took things in a slightly different direction by upping the audio streaming game with a technological advance called the Music Genome Project, which is “feature recognition” technology similar to what is used for face recognition in pictures. With this approach, over 450 different musical attributes or “genes” are considered when selecting the next song—genes being characteristics of music, such as gender of lead vocalist, type of groove, and so on. Pandora learns the listener’s preferences and then filters the catalog lists towards their preferences. The Pandora media player is based on an open-source app development platform called OpenLaszlo and can be accessed via any streaming media device. No downloads here!

我们现在已经与 Spotify 走到了一起。Napster 负责揭示音乐供需脱节问题，而 Spotify 则带头推动音乐流媒体和下载合法化。Spotify 通过道德呼吁年轻人放弃盗版并为他们的音乐服务付费而不是像 Napster 用户多年前那样盗版它，从而影响了音频流媒体的世界。Spotify 的目标是通过创建高级订阅者来重新发展音乐行业，这些订阅者将通过广告商和订阅者向出版商和艺术家支付更高的版税，从而帮助流媒体音频音乐业务重新获利。

We have now come full circle with Spotify. While Napster was responsible for shining the light on the music supply and demand disconnect, Spotify is leading the charge to legitimize music streaming and downloading. Spotify has impacted the world of audio streaming by making an ethical appeal to young people to abandon piracy and pay for their music service instead of pirating it like Napster users did years ago. Spotify’s goal is to re-grow the music industry by creating Premium subscribers who will help to re-monetize the streaming audio music business with higher royalty payouts to publishers and artists through advertisers and subscribers.

音乐和其他音频媒体的数字传输一直基于快速发展的技术和新的商业模式。这些相同的技术和商业模式也为流媒体视频铺平了道路。

The digital delivery of music and other audio media has been based on rapidly evolving technologies and new business models. These same technologies and business models have also paved the way for streaming video.

电视的新面孔

The New Face of Television

过去几年，随着传输方式从标准广播、有线和卫星方法扩展到包括称为互联网协议电视 (IPTV) 的传输系统，消费者可以收看的电视数量呈爆炸式增长。通过 IPTV，电视服务通过宽带 IP 网络传送或流式传输到您的家庭或移动设备。

There has been an explosion in the amount of TV available to the consumer in the last few years as the delivery methods have expanded from the standard broadcast, cable and satellite methods to include a delivery system called Internet Protocol Television, or IPTV. Through IPTV, television services are delivered or streamed over broadband IP networks to your home or mobile device.

IPTV 服务由三个主要组组成。第一组是直播电视，可能有也可能没有与当前电视节目相关的社交媒体互动。时移电视是第二组，它包含两类：重播几小时或几天前最初播出的节目的追赶电视和从头开始重播当前节目的重播电视。第三组是视频点播(VOD)，它允许观众浏览当前未播放的以前录制的视频目录。

IPTV services are comprised of three main groups. The first group is live television that may or may not have social media interactivity related to the current TV show. Time-shifted television is the second group that contains two categories: catch-up TV which replays a show that was initially broadcast hours or days ago and start-over TV which replays the current show from its beginning. The third group is Video on Demand (VOD), which allows the viewer to browse a catalog of previously recorded videos that are not being broadcast at the moment.

专业的流媒体视频服务，例如 Amazon Instant Video、Netflix、Hulu Plus、Crackle 和 Blockbuster On Demand，适合时移和 VOD 组，让消费者可以在需要时自由观看电影和电视节目。设备。

Professional streaming video services, such as Amazon Instant Video, Netflix, Hulu Plus, Crackle and Blockbuster On Demand, fit into the time-shifted and VOD groups that offer the consumer the freedom to watch movies and TV shows when they want on a multitude of devices.

图 21.4 手机上的音乐会拍摄事件

Figure 21.4 Concertgoer Shooting Event on Mobile Phone

除了提供专业制作的内容外，YouTube、Vimeo、Facebook 和 Flickr 等社交媒体网站还允许消费者分享他们自己使用廉价网络摄像头、数码相机和手机制作的视频内容（图 21.4 ）。截至 2014 年，这种由消费者驱动的内容占全球互联网总流量的 87%。这种用户生成的内容与 IPTV 传送系统相结合，导致年轻观众对旧广播服务失去兴趣，这反过来又导致广播公司彻底修改其商业模式以增加观众。

In addition to the professionally created content available, social media sites such as YouTube, Vimeo, Facebook, and Flickr, allow consumers to share their own video content created with inexpensive webcams, digital cameras and their mobile phones (Figure 21.4). As of 2014, this consumer-driven content represented 87 percent of the total Internet traffic worldwide. This user-generated content, combined with the IPTV delivery systems, is causing younger audiences to lose interest in the old broadcasting services, which in turn is causing broadcasters to completely revise their business models to increase their audience.

广播电视和有线电视进入流媒体

Broadcast TV and Cable Goes Streaming

在 20 世纪下半叶，有线电视与广播电视一起稳步增长。当卫星电视在 20 世纪 70 年代后期出现时，它成为一种竞争选择，争夺收视率和家庭。但由于视频现在作为流媒体传输，内容提供商（例如 ABC、CBS、HBO 等）的目标正在从家庭传输转变为让观众随时随地访问内容他们想看到它。媒体和有线电视公司的高管们将此视为一个商机，可以绕过有线电视和卫星电视公司，通过流媒体视频直接向消费​​者销售点播节目，从而赚取更多利润。

Cable television saw a steady growth, alongside broadcast television, over the second half of the 20th Century. When satellite TV came on the scene in the late 1970s, it became a competitive option and vied for viewership and households. But since video is now being delivered as streaming media, the goal of content providers, such as ABC, CBS, HBO, and so on, is shifting from household delivery to giving viewers access to content whenever and however they want to see it. The media and cable executives are seeing this as a business opportunity to make more money by selling à la carte programming via streaming video directly to the consumer, bypassing the cable and satellite companies.

看电视的人群也在发生变化。年轻的观众不太可能订阅成本更高的有线或卫星套餐来观看他们最喜欢的节目，尤其是在 Hulu 和 Netflix 等便宜得多的流媒体网站上提供所有节目的情况下。为此，HBO 宣布，他们将在 2015 年开始以远低于有线和卫星捆绑费用的价格出售他们的电影和节目的仅互联网订阅。这样，只对观看特定节目（如“权力的游戏”或“女孩”）感兴趣的观众可以通过在线订阅直接观看 HBO 节目，而无需购买数十个不需要的频道。CBS 还宣布他们将开始在线销售他们的节目，每月收取少量费用。但是，CBS 将保留直播活动，

The television viewing demographics are also shifting. Younger audiences are less likely to subscribe to a higher cost cable or satellite package to view their favorite shows, especially with all of the programming out there on far less expensive streaming media sites such as Hulu and Netflix. To this end, HBO has announced that in 2015 they will start selling an Internet-only subscription to their movies and shows far below the price point of cable and satellite bundling fees. This way viewers who are only interested in watching specific programs, such as “Game of Thrones” or “Girls,” can get the HBO shows directly via an online subscription without having to purchase dozens of unwanted channels. CBS has also announced that they will begin selling their programming online for a small monthly fee. However, CBS will withhold live events, such as pro football, from its “CBS All Access” subscription because sports are a huge ad revenue generating income stream.

流媒体设备

Streaming Media Devices

本书付印时，美国约有 760 万家庭已经从观看传统的广播、有线或卫星电视转变为通过 Wi-Fi 到电视机的流媒体互联网观看节目和电影。而且，随着 Hulu Plus、Netflix、Amazon Instant、Spotify 和 Pandora 等流媒体服务的兴起，DVD 和 CD 等基于磁盘的媒体的时代开始消退。

When this book went to press, about 7.6 million households in the United States have made the shift from watching traditional broadcast, cable or satellite television to viewing their programs and movies over the streaming Internet via Wi-Fi to their TV sets. And, with the rise of streaming media services such as Hulu Plus, Netflix, Amazon Instant, Spotify and Pandora, the days of disk-based-media like DVDs and CDs are beginning to wane.

有许多类型的流媒体设备可用——例如流媒体盒（Roku3、Apple TV 和 Amazon Fire TV） 100 美元，谷歌 Chromecast 等游戏机，Xbox360、Playstation 3 和 Wii 等游戏机，智能电视、平板电脑、智能手机、家庭影院设备和蓝光播放器——所有这些都能够向消费者提供流媒体内容（图 21.5）。这些设备中的一些设备从网络流式传输媒体，而其他设备也能够显示来自消费者本地媒体收藏的媒体。

There are many types of streaming media devices available—such as streaming boxes (Roku3, Apple TV and Amazon Fire TV) for under $100, sticks such as Google’s Chromecast, game consoles such as Xbox360, Playstation 3 and Wii, Smart TVs, tablets, smart phones, home theater devices and Blu-ray players—all of which are capable of delivering streaming media content to the consumer (Figure 21.5). Some of these devices stream media from the web while others are also capable of displaying media from the consumer’s local media collection as well.

图 21.5 流媒体设备

Figure 21.5 Streaming Media Devices

无论使用何种设备，它们都可以播放 1080p 的视频，并且具有相同的 VOD 服务、播放音乐和游戏的能力，而其他设备则可以播放直播流媒体事件。Amazon Fire TV 等一些设备凭借附加功能脱颖而出，例如 8 GB 板载存储空间、声控遥控器、四核处理器、2 GB 内存和非常适合游戏的专用 GPU，以及杜比数字环绕声和光纤音频输出。

No matter the device, they all play video at 1080p and have in common the same VOD services, the ability to play music and games, while still others can play live streaming events. Some devices such as the Amazon Fire TV, stand out with additional features like 8 GB of on-board storage space, a voice activated remote control, quad-core processors, 2 GB of memory with a dedicated GPU that is great for gaming, plus Dolby Digital surround sound and optical audio outputs.

相比之下，谷歌的 Chromecast，被称为棒，看起来像一个小型 USB 拇指驱动器，但它实际上是一个加密狗，这是一个包含安全软件的小硬件，只有当设备插入计算机或已在 Chromecast 中注册的高清电视。Chromecast 也不是独立设备，因为它需要智能手机、平板电脑或 PC 等移动设备才能观看流媒体视频。

In contrast, Google’s Chromecast, referred to as a stick, looks like a small USB thumb drive but it is actually a dongle which is a small piece of hardware that contains secured software that will only run when the device is plugged in to a computer or an HDTV that has been registered with Chromecast. Chromecast is also not a standalone device, as it requires a mobile device like a smartphone, tablet, or PC in order to watch streaming video.

流媒体设备的快速发展与传输技术的快速发展相结合，不仅为当今的娱乐观众提供了广泛的视频节目选择，还提供了观看设备。这些设备可以是固定的，如电脑和电视，也可以是移动设备，如智能手机和平板电脑，从而显着增加流媒体的观看选择和消费。

The rapid evolution of streaming media devices has joined with the rapid evolution in the delivery technologies to provide todays’ entertainment viewer with a wide range of not just video programming options, but viewing devices. These devices can be either fixed like computers and TVs or mobile devices like smart phones and tablets, thereby dramatically increasing both the viewing options and the consumption of streaming media.

概括

Summary

总而言之，如今有许多交付方法可用于接收流媒体内容和许多能够显示该内容的互联网连接设备——从计算机到智能手机和智能电视、平板电脑、游戏机、机顶盒、DVD 播放器等等中间。随着计算机处理能力的技术进步、传输系统和播放器的标准化、视频和音频压缩编解码器的高度改进以及互联网的爆炸式增长，流媒体的能力已成为一种普遍现象。

In summary, there are many delivery methods available today used to receive streaming content and many Internet-connected devices capable of displaying that content—from computers to smart phones and smart TVs, tablets, gaming consoles, set-top boxes, DVD players and everything in-between. With technological advances in computer processing power, standardization of delivery systems and players, highly improved video and audio compression codecs and the explosive growth of the Internet, the ability to stream media has become a commonplace phenomenon.

流媒体有望改变广播和有线电视的格局。敬请期待！

Streaming media promises to change the landscape of broadcast and cable television. So stay tuned!